v0.3.3: Rate limiting, IPv6 fix, schema versioning, video preload, engagement propagation

Security & stability:
- Incoming auth-fail rate limiting per source IP (3 attempts, then exponential backoff)
- Schema versioning via PRAGMA user_version with migration framework

Networking:
- IPv6 http_addr fix: advertise actual public IPv6 instead of 0.0.0.0
- N2/N3 TTL reduced from 7 days to 5 hours
- Full N1/N2 state re-broadcast every 4 hours
- Bootstrap isolation recovery: 24h check with sticky N1 advertising
- Bidirectional engagement propagation (upstream + downstream)
- Auto downstream registration on pull sync and push notification
- post_upstream table for CDN tree traversal

Media & UI:
- Video preload="auto" for share links and in-app blob URLs
- Following: Online/Offline split with last-seen timestamps
- DMs filtered from My Posts tab
- Image lightbox, audio player, file attachments with download prompt
- Share link unroutable address filtering

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/app.js

@@ -1644,6 +1644,7 @@ async function loadPostMedia(container) {
         const mime = vid.dataset.mime || 'video/mp4';
         try {
             vid.src = await loadBlobAsObjectUrl(cid, postId, mime);
+            vid.preload = 'auto';
         } catch (e) {
             vid.poster = '';
             vid.insertAdjacentHTML('afterend', '<span class="empty-hint">Video unavailable</span>');