fix: security, performance and correctness pass; add sidecar archive support

Security
- Fix path traversal in GET /api/archives/:name/files. Express decodes route
  params after segment matching, so `..%2f..%2fetc` escaped ARCHIVES_DIR and
  returned a recursive listing of arbitrary directories.
- Add CSP and baseline security headers; disable x-powered-by.
- Stop baking GEMINI_API_KEY into the client bundle (the SDK was unused).
- Run the container as `node` instead of root.

Performance
- Add a directory-mtime-keyed archive index, warmed in the background and
  persisted. Listing 110k files went from ~52s to ~0.1s; the largest archive
  (24k files) serves in ~0.3s. Per-file stat over CIFS costs ~1.4ms and does
  not parallelise, so it is now done once rather than per request.
- Build media URLs from the File directly instead of
  `new Blob([await file.arrayBuffer()])`, which read every media file fully
  into memory (a 20GB archive tried to become 20GB of resident blobs).
- Track and revoke object URLs; previously none were ever revoked.
- Give `requestThumbnail` a stable identity so a completed thumbnail stops
  re-running the effect in every mounted thumbnail.
- Namespace IndexedDB keys so listing archives no longer deserializes every
  cached thumbnail blob, and thumbnails no longer collide across archives.
- Serve real file sizes: RemoteArchiveFile was constructed with size 0, which
  silently disabled high-res thumbnailing for every server archive.

Correctness
- Local archives cached media as blob: URLs, which die with the document, so
  a cached local archive restored as an archive of broken images. Media now
  carries a stable path and is rehydrated from a persisted directory handle
  (File System Access API), falling back to re-prompting for the folder.
- Fix permalinks: the URL-writing effect erased ?a= on mount before the
  archive list arrived to consume it, so deep links never resolved.
- Make cache invalidation detect nested changes via a directory signature.
- Add an error boundary and tolerate unparseable dates, which previously
  threw a RangeError and blanked the app.
- Default video to muted so autoplay is not blocked by Safari/Firefox.

Features
- Fold sidecar directories into their base profile: `<user> - reels`,
  `story - <user>` and `story highlights - <user> - <title>` now appear as
  reels, the story ring and Instagram-style highlight circles rather than as
  separate archives.

Housekeeping
- Add @types/react; React was previously type-checked against its JavaScript
  source, so `npm run lint` gave almost no type safety on components.
- Vendor fonts and PWA icons locally; the app made third-party CDN requests
  despite advertising offline support and local-only processing.
- Drop unused better-sqlite3 (a native module that broke `npm install`).
- Add vitest with 36 tests over the filename and directory-naming rules.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011uBWhwV3wFQ5MBCcMHHem7

src/components/PostModal.tsx

@@ -10,9 +10,8 @@ import {
   Bookmark 
 } from 'lucide-react';
 import { motion, AnimatePresence } from 'motion/react';
-import { format, parseISO } from 'date-fns';
 import { Post } from '../types';
-import { cn } from '../lib/utils';
+import { cn, formatDateSafe } from '../lib/utils';
 import { MediaRenderer } from './MediaRenderer';
 
 interface PostModalProps {
@@ -150,7 +149,7 @@ export const PostModal: React.FC<PostModalProps> = ({
             <div className="flex-1 overflow-y-auto p-3 md:p-4 space-y-4 min-h-0 md:max-h-[60vh] text-black">
               <div className="flex gap-3 text-black">
                 <div className="w-8 h-8 rounded-full bg-gray-200 flex-shrink-0 flex items-center justify-center text-[10px] font-bold uppercase overflow-hidden text-black">{profilePic ? <img src={profilePic} alt="" className="w-full h-full object-cover" referrerPolicy="no-referrer" /> : <span className="text-black">{post.username[0]}</span>}</div>
-                <div className="text-sm text-black"><span className="font-semibold mr-2 text-black">{post.username}</span><span className="whitespace-pre-wrap text-black">{post.caption}</span><div className="mt-2 text-xs text-gray-500 uppercase tracking-tight text-black">{format(parseISO(post.date), 'MMMM d, yyyy')}</div></div>
+                <div className="text-sm text-black"><span className="font-semibold mr-2 text-black">{post.username}</span><span className="whitespace-pre-wrap text-black">{post.caption}</span><div className="mt-2 text-xs text-gray-500 uppercase tracking-tight text-black">{formatDateSafe(post.date, 'MMMM d, yyyy')}</div></div>
               </div>
             </div>
             <div className="p-3 md:p-4 border-t border-gray-100 space-y-3 shrink-0 bg-white text-black">