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/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
-    const savedNetwork = localStorage.getItem('waste_last_network')
-    if (savedNetwork) doJoin(savedNetwork, '')
+    // 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