Integrate group files: nullable room for uploads, archive class, claim idempotency, upload route

Wires the three parallel group-cloud tracks to one surface and fixes the
seams between them:

- chat_media_archive.room_id becomes nullable (direct web uploads have no
  Matrix room yet — the contract's null-event pattern extends to the room);
  core GroupFile.roomId and ArchiveEntryInput.roomId follow.
- mime_class gains 'archive' (zip) across the 029 CHECK, validation
  MIME_CLASSES and the bot classifier — one vocabulary everywhere.
- registerArchiveEntry claim keys are null-safe for room-less uploads.
- New: POST /files/groups/:groupId/upload — FileInterceptor (20 MiB) streams
  through magic-byte sniffing, library-safe naming, oCIS upload and the
  metadata index, behind group-membership ACL (Owner/Admin bypass).
- safeFileName/sniffMime promoted to packages/core (file-names.ts,
  file-mime.ts) so the bot and the api share one implementation; the bot's
  local modules become re-export shims; @types/node added to core.

Verified: api typecheck clean, group-files 22/22, bot 74/74, web typecheck
clean; 029 re-applied clean on a fresh scratch DB (room_id nullable,
archive class, claim_key unique all confirmed in the catalog).

apps/api/src/group-files/group-files.validation.ts

@@ -13,11 +13,13 @@
  * `any`, and DB CHECK constraints (029) are coarse backstops only.
  */
 import { BadRequestException } from "@nestjs/common";
+import { MIME_CLASSES } from "@tactical-media-broadcast-hub/core";
 import type {
   FileRetention,
   GroupFile,
   GroupFileMapping,
   MatrixAttachmentCandidate,
+  MimeClass,
   SharedFileOrigin,
 } from "@tactical-media-broadcast-hub/core";
 
@@ -29,8 +31,7 @@ export type RetentionMode = (typeof RETENTION_MODES)[number];
 export const ORIGIN_KINDS = ["matrix", "bridge", "upload", "pad-export"] as const;
 export type OriginKind = (typeof ORIGIN_KINDS)[number];
 
-export const MIME_CLASSES = ["image", "video", "audio", "document", "other"] as const;
-export type MimeClass = (typeof MIME_CLASSES)[number];
+export { MIME_CLASSES, type MimeClass };
 
 export const FILE_STATUSES = ["available", "revoked", "expired"] as const;
 export type FileStatus = (typeof FILE_STATUSES)[number];