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>

crates/core/src/http.rs

@@ -474,7 +474,7 @@ pub fn render_post_html(post: &crate::types::Post, _post_id: &[u8; 32], author_n
         let cid_hex = hex::encode(&att.cid);
         if att.mime_type.starts_with("video/") {
             attachments_html.push_str(&format!(
-                r#"<video src="/b/{}" controls style="max-width:100%;margin:0.5rem 0;border-radius:8px"></video>"#,
+                r#"<video src="/b/{}" controls preload="auto" playsinline style="max-width:100%;margin:0.5rem 0;border-radius:8px"></video>"#,
                 cid_hex
             ));
         } else {