v0.6.0 — Ember

### Added

- `watchfire chat` CLI command — dedicated command to start an interactive chat session with full project context
- **Cross-platform sandbox abstraction** — shared `SandboxPolicy` with platform-specific backends: macOS Seatbelt, Linux Landlock (kernel 5.13+) / bubblewrap (fallback)
- **Landlock sandbox** (Linux) — zero-dependency kernel-based sandboxing using `go-landlock`, daemon re-invokes itself as helper to apply restrictions before exec
- **Bubblewrap sandbox** (Linux) — namespace-based isolation with read-only root, writable project dir, hidden credential dirs
- `--sandbox ` and `--no-sandbox` CLI flags on `run`, `chat`, `plan`, `generate`, `wildfire` commands
- Sandbox backend configurable per-project (`project.yaml`) and globally (`settings.yaml`)
- System tray icon abstraction for Linux — `setTrayIcon()` helper dispatches between macOS template icons and Linux standard icons
- **Windows build support** — CLI and daemon compile and run on Windows (unsandboxed, no POSIX signal dependencies)
- **Windows notifications** — toast notifications via `beeep` library
- Platform-aware updater asset names — supports `watchfire--[.exe]` format

### Fixed

- Agent chaining not stopping on auth (401) or rate-limit (429) errors — start-all/wildfire mode now checks for active issues before spawning the next agent
- Linux notification double-close bug — `notify_linux.go` now properly handles file close errors

### Changed

- Default sandbox changed from `"sandbox-exec"` to `"auto"` — platform auto-detects best backend
- Sandbox setting priority: CLI flag > project setting > global default