Add group cloud: files index api, web UI, archive sync bot

The Telegram-like group file contract (packages/core shared-files.ts) becomes
a working subsystem, built in three parallel tracks:

API (NestJS): migration 029 group_files (chat_media_archive metadata-only
index with partial replay-unique + RLS, group_file_shares with sha256 token
persistence, archive_sync_state/outbox durable-claim seam incl. a unique
claim_key index), group-files module (list/search with cursor pagination,
direct upload ≤20 MiB streamed+hashed to oCIS WebDAV, download with ACL +
retention rechecks, share links with expiry, retention modes incl.
legalHold) — RBAC group-membership authz + audit chain events.

Web: Files section per group — group picker, drag-drop upload (20 MiB cap),
search + MIME/origin filters, cursor pagination, download via authenticated
blob fetch, share dialog with expiry + shown-once token, admin retention
dialog; bilingual EN/ES (wiki i18n pattern); nav sidebar/palette/bottom-nav
wiring; MIME classes aligned to the DB CHECK (document/other).

Archive bot (apps/archive-bot): plain sync-loop Matrix bot mirroring
attachments from explicitly-mapped unencrypted archive rooms — raw /sync
with durable since-cursor, outbox-claimed ingestion (hash-verified stream,
no temp files), magic-byte MIME sniffing, safe-name normalization, WebDAV
upload, indexed + replied with link, redaction→unavailable; health endpoint;
Dockerfile. Tests 74/74, typecheck clean across api/web/bot.

apps/web/src/app/(main)/layout.tsx

@@ -15,7 +15,7 @@ import { useIsMobile } from "../../hooks/use-is-mobile";
 const titles: Record<string, string> = {
   streams: "Home", search: "Search", inbox: "Inbox", approvals: "Approvals", more: "More", compose: "New post",
   calendar: "Calendar", video: "Video", analytics: "Analytics", connections: "Connections", team: "Team",
-  audit: "Audit log", onboarding: "Welcome", settings: "Settings", archive: "Archive",
+  audit: "Audit log", onboarding: "Welcome", settings: "Settings", archive: "Archive", files: "Files",
 };
 const rootTabs = new Set(["/streams", "/search", "/inbox", "/more"]);
 const scrollPositions = new Map<string, { main: number; nested: number[] }>();