feat(web): load a real chat after Nuri wallet login

[eminogrande]

Problem

After a successful Nuri Connect + Passkey Wallet login, the web root renders the existing repository browser. Users see This community is empty because web/src/app/routes/index.tsx mounts ReposPage; this is not a chat screen.

Production also currently has zero channels and zero active channel memberships, so a chat UI alone would still have nothing to open.

Scope

1. Replace the authenticated root content with a browser-native Buzz chat: channel sidebar, selected-channel timeline, empty/error/loading states, and text composer. Preserve the repository browser under /repos.
2. Use the existing Buzz/Nostr protocol and unlocked in-memory Nuri signer: discover membership (39002) and metadata (39000), join an open channel (9021), query/subscribe to messages (9, 40002), and publish text messages (9) over NIP-42-authenticated WebSocket with relay OK handling.
3. Provision one open production #general channel through the existing relay owner, verify a newly registered Nuri user can join/read/send/live-receive, retain /inbox, and pass web unit/type/lint/build/smoke checks.

What we are not doing

• Full Tauri desktop UI port
• Threads, reactions, file uploads, huddles, moderation, agent panels, or forum channels
• Persisting the Nostr private key outside tab memory
• Bypassing closed-relay membership or Connect verification

Security invariants

• Continue using the nuri-expo-wallet-v1 signer already unlocked by NuriWalletGate.
• Private key remains tab-memory-only and is best-effort zeroized on lock/pagehide.
• NIP-42 authentication and relay membership remain mandatory.
• Channel join and messages are signed by the user key; no server impersonation.

References

• Session: @session:default/20260724_150854_84a994
• Branch: feat/nuri-web-chat
• Created by: Hermes Agent via emin-mcp
• Existing integration: feat(web): use Nuri passkey wallet as Buzz identity #1 and PR feat: use Nuri passkey wallets as Buzz identities #2

[eminogrande]

Reopening because the Production acceptance criteria in this issue are not complete yet: chat.nuri.com is not serving the browser chat and Production has zero channels. The current focused fix removes the automatic post-Connect WebAuthn call and requires a user click, preventing Safari/WebKit not focused failures. Deployment remains limited to the basic chat and one real open #general; multi-Space work is excluded.