fix: resolve UI state reset and backlog sync hang

- Fix client startup order: fetch/apply server UI state BEFORE loadGuilds() to prevent overwriting persisted state with default guild
- Remove auto-post of first guild in loadGuilds() — let server state drive selection
- Refactor collectWatchableChannels() to collect text channels fast first, then discover threads in parallel with 5s per-channel timeout and 30s overall timeout to prevent blocking message sync
- Ignore /favicon.ico 404 in error logging to reduce noise

Fixes:
- UI state now persists across restart (was being overwritten by client startup race)
- Backlog sync no longer hangs on thread discovery (was blocking before message sync)
- Cleaner logs without favicon 404 errors

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/webserver.ts

@@ -129,6 +129,7 @@ export function startWebserver(
     }
     res.on("finish", () => {
       if (req.originalUrl.startsWith("/.well-known/appspecific/")) return;
+      if (req.originalUrl === "/favicon.ico") return;
       if (res.statusCode >= 400) {
         logger.error(
           { method: req.method, url: req.originalUrl, statusCode: res.statusCode },