feat: multi-network join, persistence, and switching in web UI

- Sidebar: "+" button next to Networks opens an inline join form;
  in browser mode shows anchor URL field; saves to waste_saved_networks
- Onboarding: saved networks shown as quick-join chips above the join
  form; auto-rejoin all saved networks on reconnect (not just one)
- Browser mode: networks persisted as [{name, anchor}] array in
  localStorage (waste_saved_networks); legacy waste_last_network kept
  for backward compat
- Daemon mode: daemon already tracks joined networks; web UI just needs
  the "+" to send join_network for additional ones

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

web/src/App.css

@@ -33,6 +33,10 @@ input:focus { border-color: var(--accent); }
 .onboarding-section { width: 100%; border-top: 1px solid var(--border); padding-top: 12px; }
 .join-form { display: flex; flex-direction: column; gap: 8px; width: 100%; }
 .join-label { font-size: 11px; text-transform: uppercase; letter-spacing: 0.08em; color: var(--muted); }
+.saved-networks { display: flex; flex-direction: column; gap: 6px; width: 100%; }
+.saved-network-chips { display: flex; flex-wrap: wrap; gap: 6px; }
+.network-chip { background: var(--surface); border: 1px solid var(--border); color: var(--text); border-radius: 20px; padding: 4px 14px; font-size: 13px; }
+.network-chip:hover { border-color: var(--accent); color: var(--accent); background: var(--surface); }
 button.primary { background: var(--accent); width: 100%; padding: 8px; font-size: 14px; }
 .toggle-link { background: none; color: var(--muted); font-size: 12px; padding: 4px 0; text-align: left; }
 .toggle-link:hover { color: var(--text); }

web/src/components/Sidebar.tsx

@@ -32,10 +32,13 @@ export function Sidebar() {
     networks, activeNetworkId, activeRoom,
     connectedPeers, peerStatus,
     setActiveRoom, setActiveNetwork, messages, browseFiles, sendFileTo, adapterMode,
-    customRooms, createRoom, logout,
+    customRooms, createRoom, logout, send,
   } = useWaste()
   const [addingRoom, setAddingRoom] = useState(false)
   const [newRoomName, setNewRoomName] = useState('')
+  const [addingNetwork, setAddingNetwork] = useState(false)
+  const [newNetName, setNewNetName] = useState('')
+  const [newNetAnchor, setNewNetAnchor] = useState('')
 
   const netCustomRooms = activeNetworkId ? (customRooms[activeNetworkId] ?? []) : []
   const rooms = ['general', ...netCustomRooms]
@@ -50,6 +53,25 @@ export function Sidebar() {
     setAddingRoom(false)
   }
 
+  function submitNewNetwork(e: React.FormEvent) {
+    e.preventDefault()
+    const name = newNetName.trim()
+    if (!name) return
+    if (adapterMode === 'browser') {
+      // Persist to saved networks list in localStorage.
+      const anchor = newNetAnchor.trim() || localStorage.getItem('waste_anchor_url') || ''
+      const saved: Array<{name: string; anchor: string}> = JSON.parse(localStorage.getItem('waste_saved_networks') ?? '[]')
+      if (!saved.some(n => n.name === name && n.anchor === anchor)) {
+        saved.push({ name, anchor })
+        localStorage.setItem('waste_saved_networks', JSON.stringify(saved))
+      }
+    }
+    send({ type: 'join_network', network_name: name })
+    setNewNetName('')
+    setNewNetAnchor('')
+    setAddingNetwork(false)
+  }
+
   const displayAlias = localPeer?.alias ?? masterAlias ?? ''
   const displayId = localPeer?.id ?? masterId ?? ''
   const card = displayId ? makeYawCard(displayId, displayAlias) : null
@@ -95,9 +117,12 @@ export function Sidebar() {
       <div className="sidebar-section">
         <div className="sidebar-label-row">
           <span className="sidebar-label">Networks</span>
+          <span style={{ display: 'flex', gap: 2 }}>
             {activeNetworkId && (
-            <button className="sidebar-add" onClick={copyHangLink} title="Copy hang link (pre-fills join form, no invite required)">🔗</button>
+              <button className="sidebar-add" onClick={copyHangLink} title="Copy hang link">🔗</button>
             )}
+            <button className="sidebar-add" onClick={() => setAddingNetwork(v => !v)} title="Join network">+</button>
+          </span>
         </div>
         {networks.map(n => (
           <button
@@ -108,6 +133,26 @@ export function Sidebar() {
             {n.network_name}
           </button>
         ))}
+        {addingNetwork && (
+          <form className="sidebar-new-room" onSubmit={submitNewNetwork}>
+            <input
+              autoFocus
+              value={newNetName}
+              onChange={e => setNewNetName(e.target.value)}
+              placeholder="network name"
+              onKeyDown={e => e.key === 'Escape' && (setAddingNetwork(false), setNewNetName(''))}
+            />
+            {adapterMode === 'browser' && (
+              <input
+                value={newNetAnchor}
+                onChange={e => setNewNetAnchor(e.target.value)}
+                placeholder="anchor URL (blank = current)"
+                className="mono"
+                style={{ fontSize: '0.75rem', marginTop: 4 }}
+              />
+            )}
+          </form>
+        )}
       </div>
 
       <div className="sidebar-section">

web/src/pages/Onboarding.tsx

@@ -72,8 +72,15 @@ export function Onboarding({ status }: Props) {
     if (adapterMode !== 'browser' || status !== 'connected') return
     const { network: n, netHash: nh } = parseInviteParams()
     if (n || nh) return // explicit invite — don't auto-join, show form
+    // Rejoin all saved networks.
+    const saved: Array<{name: string; anchor: string}> = JSON.parse(localStorage.getItem('waste_saved_networks') ?? '[]')
+    if (saved.length > 0) {
+      saved.forEach(s => doJoin(s.name, ''))
+    } else {
+      // Legacy single-network fallback.
       const savedNetwork = localStorage.getItem('waste_last_network')
       if (savedNetwork) doJoin(savedNetwork, '')
+    }
   }, [adapterMode, status]) // eslint-disable-line react-hooks/exhaustive-deps
 
   function joinNetwork(e: React.FormEvent) {
@@ -87,8 +94,16 @@ export function Onboarding({ status }: Props) {
     if (adapterMode === 'browser') {
       localStorage.setItem('waste_anchor_url', anchorUrl)
       if (nick.trim()) localStorage.setItem('waste_nick', nick.trim())
-      if (name) localStorage.setItem('waste_last_network', name)
-      else localStorage.removeItem('waste_last_network')
+      if (name) {
+        // Persist to saved networks list.
+        const saved: Array<{name: string; anchor: string}> = JSON.parse(localStorage.getItem('waste_saved_networks') ?? '[]')
+        if (!saved.some(n => n.name === name)) {
+          saved.push({ name, anchor: anchorUrl })
+          localStorage.setItem('waste_saved_networks', JSON.stringify(saved))
+        }
+        // Keep legacy key for backward compat.
+        localStorage.setItem('waste_last_network', name)
+      }
     }
 
     if (hash.length === 64 && !name) {
@@ -121,6 +136,7 @@ export function Onboarding({ status }: Props) {
   }
 
   const shortId = masterId ? masterId.slice(0, 16).replace(/(.{4})/g, '$1 ').trim() : null
+  const savedNetworks: Array<{name: string; anchor: string}> = JSON.parse(localStorage.getItem('waste_saved_networks') ?? '[]')
 
   // ── disconnected / connecting ────────────────────────────────────────────────
   if (status !== 'connected') {
@@ -159,8 +175,21 @@ export function Onboarding({ status }: Props) {
         </div>
       )}
 
+      {adapterMode === 'browser' && savedNetworks.length > 0 && (
+        <div className="saved-networks">
+          <span className="join-label">Saved networks</span>
+          <div className="saved-network-chips">
+            {savedNetworks.map(n => (
+              <button key={n.name} className="network-chip" type="button" onClick={() => doJoin(n.name, '')}>
+                {n.name}
+              </button>
+            ))}
+          </div>
+        </div>
+      )}
+
       <form onSubmit={joinNetwork} className="join-form">
-        <label className="join-label">Join a network</label>
+        <label className="join-label">{savedNetworks.length > 0 ? 'Join another network' : 'Join a network'}</label>
 
         {adapterMode === 'browser' && (
           <input