feat(maestro-tui): ratatui widgets + render orchestration (NAP-280)

Adds the full visual layer:

- `state.rs` — `AppState` (tabs/focus/mode/sidebar visibility/overlay).
  v1 keeps each tab to one optional session; the split tree is v1.5.
- `terminal.rs` — `TerminalGuard` (raw mode + alt screen + mouse capture
  with RAII restore) and an idempotent panic hook that restores the
  terminal before re-panicking.
- `sidebar.rs` — daemon → session tree with ●/○/✗ glyphs. Pulls a label
  out of `metadata.label` (the protocol's shape), falls back to the
  command.
- `tabs.rs` — top-row TabBar with active highlight.
- `pane.rs` — `vt100::Screen` → ratatui `Buffer` cell-by-cell, with full
  fg/bg/bold/italic/underline/reverse translation. `PaneStatus` round-trips
  from `SessionState`.
- `overlays.rs` — SpawnModal (5-field form with rotation), KillConfirm,
  HelpOverlay, Toast. All centered popups with `Clear` underlay.
- `render.rs` — `draw(f, RenderInputs)` composes everything; returns a
  `RegionMap` whose `region_at(col, row)` resolves a mouse coordinate to
  a tagged Region (modal eclipses the rest).

22 new unit tests bringing the crate total to 80 passing. Tests use
content-based assertions over `ratatui::backend::TestBackend` output rather
than file-based goldens — less brittle to whitespace shifts while still
covering the visible content.

Cargo.toml

@@ -38,6 +38,7 @@ toml = "0.8"
 tracing = "0.1"
 tracing-subscriber = { version = "0.3", features = ["env-filter"] }
 uuid = { version = "1", features = ["v4", "serde"] }
+ratatui = "0.28"
 vt100 = "0.15"
 
 [profile.release]