fix(tui): prioritize composer keybinds - #42384

What

Replace the Shell tab's hard-coded Ctrl+D interceptor with OpenTUI keymap layer priority for the full composer.

Closes #42377.

Before / After

Before: #42366 restored the default Shell kill shortcut with a raw event interceptor that recognized only literal Ctrl+D. Custom bindings and the adjacent composer navigation/Subagents layers still depended on equal-priority registration order against focused-editor bindings.

After: Composer navigation and active tab actions use contextual priority. Their configured bindings win while the composer is active, including custom bindings, without matching physical keys manually.

How

• Give the composer navigation layer contextual priority: 1.
• Give Shell and Subagents action layers the same priority.
• Remove the Shell-specific raw event interceptor.
• Extend the composer keymap test to exercise tab navigation and a custom Shell kill binding while a textarea remains focused.

Investigation

Focused rendered-component tests showed permission rejection, textual forms, autocomplete destructive actions, and ordinary non-default editor collisions already behave correctly. Lowering app.exit priority did not fix the real TUI. Applying priority to the active composer layers did.

Testing

• bun run test test/cli/tui/composer-keymap.test.tsx from packages/tui: 3 passed
• bun typecheck from packages/tui: passed
• Push hook repository typecheck: 34 packages passed
• Live PTY with termctrl against the elected service: opened composer, switched Subagents → Shell, pressed Ctrl+D, observed the shell disappear, and confirmed its ID was absent from /api/shell

Flow

flowchart LR
    Key[Configured keypress] --> Mode{Composer active?}
    Mode -- no --> Editor[Normal global/editor binding]
    Mode -- yes --> Priority[Priority 1 composer layer]
    Priority --> Action[Navigation or active-tab action]