Add MLOps feature store, fix UI layout, add docs and Gitea remote

Backend:
- Replace on-the-fly Ollama calls with versioned feature store (task_features, task_edges)
- Background Tokio worker drains pending rows; write path returns immediately
- MLConfig versioning: changing model IDs triggers automatic backfill via next_stale()
- AppState with FromRef; new GET /api/ml/status observability endpoint
- Idempotent mark_pending (content hash guards), retry failed rows after 30s
- Remove tracked build artifacts (backend/target/, frontend/.next/, node_modules/)

Frontend:
- TaskItem: items-center alignment (fixes checkbox/text offset), break-words for overflow
- TaskDetailPanel: fix invisible AI context (text-gray-700→text-gray-400), show all fields
- TaskDetailPanel: pending placeholder when latent_desc not yet computed, show task ID
- GraphView: surface pending_count as amber pulsing "analyzing N tasks…" hint in legend
- Fix Task.created_at type (number/Unix seconds, not string)
- Auth gate: LoginPage + sessionStorage; fix e2e tests to bypass gate in jsdom
- Fix deleteTask test assertion and '1 remaining'→'1 left' stale text

Docs:
- VitePress docs in docs/ with guide, MLOps pipeline, and API reference

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/Cargo.toml

@@ -17,10 +17,13 @@ tokio = { version = "1", features = ["full"] }
 sqlx = { version = "0.7", features = ["runtime-tokio-rustls", "sqlite"] }
 serde = { version = "1", features = ["derive"] }
 serde_json = "1"
-tower-http = { version = "0.5", features = ["cors"] }
+tower-http = { version = "0.5", features = ["cors", "auth"] }
 uuid = { version = "1", features = ["v4"] }
 rand = "0.8"
 anyhow = "1"
+reqwest = { version = "0.11", features = ["json"] }
+futures = "0.3"
+sha2 = "0.10"
 
 [dev-dependencies]
 axum-test = "14"