feat: comprehensive project improvements

- Fix 14 Clippy warnings across server and bot-sdk
- Add 67 unit tests (32 bot-sdk, 34 server, 1 doctest)
- Add Prometheus metrics endpoint (/api/metrics)
- Add structured JSON logging (EIFELDC_LOG_FORMAT=json)
- Add release workflow (Docker push + GitHub Release + Tauri builds)
- Add rate limiting middleware (EIFELDC_RATE_LIMIT)
- Add CORS restriction (EIFELDC_CORS_ORIGINS)
- Add session token expiry (EIFELDC_SESSION_TTL)
- Add input validation (username/password/homeserver length limits)
- Add upload size limit (EIFELDC_MAX_UPLOAD_MB)
- Upgrade Tauri client from v1 to v2
- Add session store with SQLite persistence
- Add proper error types and cleanup across all crates
- Format all code with cargo fmt
- Update CI pipeline with fmt, clippy, test, frontend, and Tauri checks
- Add README with full API reference and setup guide

infra/nginx/eifeldc.conf

@@ -6,6 +6,10 @@ upstream synapse_server {
     server synapse:8008;
 }
 
+upstream livekit_server {
+    server livekit:7880;
+}
+
 server {
     listen 80;
     server_name eifeldc.local;
@@ -60,6 +64,18 @@ server {
         proxy_set_header X-Forwarded-Proto $scheme;
     }
 
+    location /livekit/ {
+        proxy_pass http://livekit_server/;
+        proxy_set_header Host $host;
+        proxy_set_header X-Forwarded-For $remote_addr;
+        proxy_set_header X-Forwarded-Proto $scheme;
+        proxy_http_version 1.1;
+        proxy_set_header Upgrade $http_upgrade;
+        proxy_set_header Connection "upgrade";
+        proxy_read_timeout 86400s;
+        proxy_send_timeout 86400s;
+    }
+
     location /api/ {
         proxy_pass http://eifeldc_server;
         proxy_set_header Host $host;