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

server/Cargo.toml

@@ -15,8 +15,17 @@ tracing = { workspace = true }
 tracing-subscriber = { workspace = true }
 reqwest = { workspace = true }
 url = { workspace = true }
-axum = { version = "0.7", features = ["ws"] }
+axum = { version = "0.7", features = ["ws", "multipart"] }
 tower = "0.4"
 tower-http = { version = "0.5", features = ["cors", "fs", "trace"] }
 chrono = { version = "0.4", features = ["serde"] }
-uuid = { version = "1", features = ["v4"] }
+uuid = { version = "1", features = ["v4"] }
+mime = "0.3"
+futures = "0.3"
+rusqlite = { version = "0.30", features = ["bundled"] }
+livekit-api = { version = "0.4", features = ["access-token"] }
+prometheus = "0.13"
+lazy_static = "1"
+
+[dev-dependencies]
+tempfile = "3"