fix: replay channel state on SPA reconnect (#61)

## Summary

When closing and reopening the SPA, channel tabs were not restored because the client relied on localStorage to remember joined channels and re-sent JOIN commands on reconnect. This was fragile and caused spurious JOIN broadcasts to other channel members.

## Changes

### Server (`internal/handlers/api.go`, `internal/handlers/auth.go`)

- **`replayChannelState()`** — new method that enqueues synthetic JOIN messages plus join-numerics (332 TOPIC, 353 NAMES, 366 ENDOFNAMES) for every channel the session belongs to, targeted only at the specified client (no broadcast to other users).
- **`HandleState`** — accepts `?replay=1` query parameter to trigger channel state replay when the SPA reconnects.
- **`handleLogin`** — also calls `replayChannelState` after password-based login, since `LoginUser` creates a new client for an existing session.

### SPA (`web/src/app.jsx`, `web/dist/app.js`)

- On resume, calls `/state?replay=1` instead of `/state` so the server enqueues channel state into the message queue.
- `processMessage` now creates channel tabs when receiving a JOIN where `msg.from` matches the current nick (handles both live joins and replayed joins on reconnect).
- `onLogin` no longer re-sends JOIN commands for saved channels on resume — the server handles it via the replay mechanism, avoiding spurious JOIN broadcasts.

## How It Works

1. SPA loads, finds saved token in localStorage
2. Calls `GET /api/v1/state?replay=1` — server validates token and enqueues synthetic JOIN + TOPIC + NAMES for all session channels into the client's queue
3. `onLogin(nick, true)` sets `loggedIn = true` and requests MOTD (no re-JOIN needed)
4. Poll loop starts, picks up replayed channel messages
5. `processMessage` handles the JOIN messages, creating tabs and refreshing members/topics naturally

closes #60

Co-authored-by: user <user@Mac.lan guest wan>
Co-authored-by: clawbot <clawbot@noreply.git.eeqj.de>
Co-authored-by: Jeffrey Paul <sneak@noreply.example.org>
Reviewed-on: #61
Co-authored-by: clawbot <clawbot@noreply.example.org>
Co-committed-by: clawbot <clawbot@noreply.example.org>

.gitignore

@@ -21,6 +21,7 @@ node_modules/
 *.key
 
 # Build artifacts
+web/dist/
 /neoircd
 /bin/
 *.exe