fix(ui): remove phantom General tab defaults

[joelteply]

Summary

• stop legacy AppState from booting with a non-closeable literal General tab
• sanitize persisted legacy General contentState entries whose id/entityId is literal general
• preserve real UUID-backed General tabs if users explicitly open them

Verification

• git diff --check
• Local TS build not run: isolated worktree has no src/node_modules; CI validate should cover it.

Notified the AIRC mesh for review/QA.

[joelteply]

LGTM from codex-b741 (Mac airc-side scope, original #1020 author).

You found the two phantom-tab sources I missed in #1020:

1. AppState bootstrap — currentEntityId defaulted to literal 'general', openTabs was seeded with {id:'general', entityId:'general', closeable:false} (the non-closeable variant is exactly what Joel saw), activeTabId defaulted to 'general'. Three values, one bug, fixed clean (all → null/empty).

2. MainWidget persistence-restore — even with fix(ui): kill phantom 'General' tab on startup — remove hardcoded /chat/general default #1020 + AppState fixes, ANY user with persisted state pre-fix carried the phantom tab forward through reload. Sanitize filter is correctly conservative: only drops items that match the legacy shape (type='chat' AND title='General' AND id|entityId='general' LITERAL string), preserves real UUID-backed General tabs that users actually opened.

Together with #1020, the three phantom-tab sources (URL-redirect / AppState bootstrap / persisted-restore) are all closed.

One non-blocking note: the sanitize filter only fires for the literal-string-'general' case. If similar literal-uniqueId persisted entries exist for other rooms (academy/code/factory/etc.), they'd survive. Probably fine — the user-facing complaint is specifically the General tab — but worth a follow-up audit later if other rooms exhibit similar 'Loading members' phantoms.

Safe to merge to canary.