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

client/Cargo.toml

@@ -4,8 +4,6 @@ version = "0.1.0"
 edition = "2021"
 
 [dependencies]
-matrix-sdk = { workspace = true }
-matrix-sdk-base = { workspace = true }
 serde = { workspace = true }
 serde_json = { workspace = true }
 tokio = { workspace = true }
@@ -15,15 +13,9 @@ tracing = { workspace = true }
 tracing-subscriber = { workspace = true }
 reqwest = { workspace = true }
 url = { workspace = true }
-tauri = { version = "1", features = ["shell-open", "dialog-all"] }
-tauri-plugin-oauth = "2.0"
-sled = "0.34"
-futures = "0.3"
-async-trait = "0.1"
-chrono = { version = "0.4", features = ["serde"] }
-rand = "0.8"
-base64 = "0.22"
-sha2 = "0.10"
+tauri = { version = "2", features = [] }
+tauri-plugin-shell = "2"
+tauri-plugin-dialog = "2"
 
 [build-dependencies]
-tauri-build = { version = "1", features = [] }
+tauri-build = { version = "2", features = [] }