tui: lower default visible chat window 200->60 (faster long-session resume) ...

The cold cost is dominated by the one-shot mount of the whole visible
window at load/switch time. 200 _ChatItemView widgets each parse Markdown,
build Content, compute height and run layout in one pass. 60 cuts that
peak ~3.3x with no loss for streaming (signature cache + throttle + render
cache keep per-token cost O(1) once mounted). Model cap (max_visible_items
* 3) follows automatically: 600 -> 180. Older items collapse into the
existing "... N earlier messages not shown" hint.

tui: bound chat history render cost (cache + visible-item cap) ...

The chat panel rebuilt every renderable on each WS event, including
per-token stream_delta — so markdown was re-parsed for the entire history
on every token and the TUI lagged as conversations grew.

- Cache renderables keyed by id(item)+signature so only the changed item
  (the streaming assistant bubble) is rebuilt per token; the rest are
  reused. Prune orphaned entries so cache stays bounded by live items.
- Add max_visible_items TUI setting (default 200): render only the last
  N items with a "… N earlier messages not shown" hint when truncated.
  Items stay in the in-memory model (non-destructive) but are not laid
  out, so per-refresh cost is constant regardless of history length.
- Rename the cache attr to _chat_render_cache to avoid collision with
  Textual Widget._render_cache, which it resets on mount.

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

Navi Code TUI: review fixes for Phase 5 ...

- Fix raw CLI session API fields (session_id/name/preview)

- Add --mouse/--no-mouse flags and persistent TUI settings coercion

- Make attach_session/apply_theme public, add ChatPanel.clear()

- Deduplicate session selection handlers and editor error handling

- Update docs and tests

Navi Code TUI: Phase 5.1 — config, mouse, themes, status ...

- Add TuiSettings persisted in ~/.navi_code/tui.json (theme, mouse, scroll_speed, diff_style, keybinds).
- TUI applies saved theme/mouse on startup; CLI gets --theme override.
- Add /themes picker with live preview and /mouse toggle command.
- Extend StatusPanel with backend URL, current theme, tokens/iter placeholders.
- Fix TuiContext.app() to use Textual active_app ContextVar.
- Add unit tests for settings, themes, and status panel.

513 passed, 1 skipped. Ruff clean.

Signed-off-by: Eugene Sukhodolskiy <eugene.sukhodolskiy@gmail.com>