feat(viking): add local server management for privacy-first deployment

- Add viking_server.rs (Rust) for managing local OpenViking server process
- Add viking-server-manager.ts (TypeScript) for server control from UI
- Update VikingAdapter to support 'local' mode with auto-start capability
- Update documentation for local deployment mode

Key features:
- Auto-start local server when needed
- All data stays in ~/.openviking/ (privacy-first)
- Server listens only on 127.0.0.1
- Graceful fallback to remote/localStorage modes

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

desktop/src-tauri/Cargo.toml

@@ -22,4 +22,9 @@ tauri = { version = "2", features = [] }
 tauri-plugin-opener = "2"
 serde = { version = "1", features = ["derive"] }
 serde_json = "1"
+tokio = { version = "1", features = ["full"] }
+reqwest = { version = "0.11", features = ["json", "blocking"] }
+chrono = "0.4"
+regex = "1"
+dirs = "5"