Add invite strings (waste: URI) for peer onboarding

- internal/invite: Encode/Decode waste:<base64json{anchor,network}>
- proto: CmdGenerateInvite + EvtInviteGenerated + InviteString field
- ipc: track active network name; handle generate_invite (returns invite
  string when joined to a network, errors if not joined or no anchor)
- daemon: --join <invite> flag — decodes anchor URL + network name,
  sets anchor and auto-joins on startup
- tui: --join <invite> flag — extracts network name, skips -network
  requirement; ctrl+i generates invite and shows it full-screen;
  Esc dismisses the invite overlay
- FUTURE.md: document multi-network derived-identity design

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

cmd/tui/main.go

@@ -18,6 +18,7 @@ import (
 	tea "github.com/charmbracelet/bubbletea"
 	"github.com/charmbracelet/lipgloss"
 
+	"github.com/waste-go/internal/invite"
 	"github.com/waste-go/internal/proto"
 )
 
@@ -114,8 +115,9 @@ type model struct {
 	viewport viewport.Model
 	vpReady  bool
 
-	status string
-	errMsg string
+	status      string
+	errMsg      string
+	invitePopup string // non-empty = show invite overlay
 }
 
 func newModel(ipcPort int, network string) model {
@@ -200,7 +202,15 @@ func (m model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 		case msg.Type == tea.KeyCtrlC:
 			return m, tea.Quit
 		case msg.Type == tea.KeyEsc:
+			if m.invitePopup != "" {
+				m.invitePopup = ""
+				return m, nil
+			}
 			return m, tea.Quit
+		case msg.String() == "ctrl+i":
+			if m.enc != nil {
+				cmds = append(cmds, sendIPC(m.enc, proto.IpcMessage{Type: proto.CmdGenerateInvite}))
+			}
 		case msg.Type == tea.KeyEnter:
 			m, cmds = m.doSend(cmds)
 		case msg.Type == tea.KeyTab:
@@ -272,6 +282,9 @@ func (m model) applyEvent(evt proto.IpcMessage) model {
 			m.peerOrder = filterIDs(m.peerOrder, pid)
 		}
 
+	case proto.EvtInviteGenerated:
+		m.invitePopup = evt.InviteString
+
 	case proto.EvtMessageReceived:
 		if evt.Message != nil {
 			msg := evt.Message
@@ -417,11 +430,31 @@ func (m model) View() string {
 	if m.errMsg != "" {
 		statusLine = styleErr.Render(" ✗ " + m.errMsg)
 	} else {
-		hint := "  tab: rooms · pgup/dn: scroll · ctrl+c: quit"
+		hint := "  tab: rooms · ctrl+i: invite · ctrl+c: quit"
 		statusLine = styleStatus.Width(m.width).Render(" " + m.status + hint)
 	}
 
-	return lipgloss.JoinVertical(lipgloss.Left, mainRow, inputBox, statusLine)
+	view := lipgloss.JoinVertical(lipgloss.Left, mainRow, inputBox, statusLine)
+
+	// ── invite popup (full-screen overlay) ───────────────────────────────────
+	if m.invitePopup != "" {
+		label := styleActive.Render("Invite — share this with anyone you want to add:")
+		code := lipgloss.NewStyle().
+			Border(lipgloss.RoundedBorder()).
+			BorderForeground(lipgloss.Color("238")).
+			Padding(0, 1).
+			Width(m.width - 6).
+			Render(m.invitePopup)
+		hint := styleStatus.Render("Esc to close  ·  ctrl+c to quit")
+		popup := lipgloss.NewStyle().
+			Width(m.width).
+			Height(m.height).
+			Align(lipgloss.Center, lipgloss.Center).
+			Render(lipgloss.JoinVertical(lipgloss.Left, label, "", code, "", hint))
+		return popup
+	}
+
+	return view
 }
 
 func (m model) renderRooms(boxH int) string {
@@ -565,12 +598,23 @@ func min(a, b int) int {
 // ── main ──────────────────────────────────────────────────────────────────────
 
 func main() {
-	ipcPort := flag.Int("ipc", 17337, "daemon IPC port")
-	network := flag.String("network", "", "network name to join on startup (required)")
+	ipcPort     := flag.Int("ipc", 17337, "daemon IPC port")
+	network     := flag.String("network", "", "network name to join on startup")
+	joinInvite  := flag.String("join", "", "waste: invite string — auto-sets the network name")
 	flag.Parse()
 
+	// --join overrides --network.
+	if *joinInvite != "" {
+		inv, err := invite.Decode(*joinInvite)
+		if err != nil {
+			fmt.Fprintln(os.Stderr, "error: invalid invite:", err)
+			os.Exit(1)
+		}
+		*network = inv.Network
+	}
+
 	if *network == "" {
-		fmt.Fprintln(os.Stderr, "error: -network is required")
+		fmt.Fprintln(os.Stderr, "error: -network or -join is required")
 		flag.Usage()
 		os.Exit(1)
 	}