feat: replace input panel with ink-text-input component

[avoidwork]

Summary

Replace the current custom InputPanel component with ink-text-input to gain built-in keyboard handling, cursor navigation, focus management, and multi-line support without manual implementation.

Motivation

The current InputPanel is purely presentational — all input handling (typing, Enter-to-send, backspace, history navigation) lives in App's single useInput hook. This approach works but requires manual implementation of every keyboard feature.

Three specific gaps:

• Better UX — cursor movement, word deletion (Ctrl+W), line clearing (Ctrl+U), text selection are not implemented
• Less code in App — input logic is scattered across the App component and should be encapsulated
• Multi-line input — the current approach would need more work; ink-text-input handles this natively

Proposed Solution

1. Add ink-text-input as a dependency
2. Replace the presentational InputPanel with an ink-text-input component
3. Move input handling (typing, Enter, backspace, history nav) from App's useInput hook into the component's event handlers
4. Wire the component's value changes back to App via a callback prop
5. Preserve existing features: history navigation, command parsing, streaming state awareness

Alternatives Considered

• Keep the current approach — minimal dependencies but manual implementation of every keyboard feature
• Build a custom input component — more control but reinvents the wheel
• Use ink-text-input — proven package, encapsulates input logic, reduces App complexity

OpenSpec Note

This project uses OpenSpec for feature development. If this request is approved, I will:

1. Run /opsx:propose to generate a full proposal with specs and tasks
2. Iterate on the design before any code is written
3. Follow the task-driven implementation workflow

Additional Context

Current Architecture

• InputPanel (src/tui/inputPanel.js) — purely presentational, renders text + blinking cursor
• App (src/tui/app.js) — owns all input handling via a single useInput hook
• Input state (inputText, historyIndex, inputFocused) managed in App component

Tradeoffs

	Current (custom)	ink-text-input
Dependency	None	+1 package
Input logic	All in App's useInput	Encapsulated in component
Focus management	Manual (inputFocused state)	Built-in
Keyboard features	Whatever implemented	Cursor nav, selection, Ctrl+W, Ctrl+U, etc.
Multi-line	Custom handling	Built-in
Control	Full	Constrained by component API

Audit Findings (for Issue #591)

• src/tui/app.js:739 — The entire input handling lives in a single useInput callback (~75 lines). This is the primary target for extraction. It handles: keystroke accumulation, Enter-to-submit, backspace, up/down history navigation, Tab for focus toggle, Escape for interrupt/quit, and onboarding input routing.
• src/tui/app.js:38-39 — Input state (inputText, historyIndex, inputFocused) is managed in App. With ink-text-input, the component would own its text state, and App would only need a callback prop (onSubmit/onChange) and a separate inputFocused state for focus/blur events.
• src/tui/app.js:778-791 — History navigation (up/down arrow) reads from chatHistory array. This logic would need to be preserved — either kept in App's onSubmit handler or wired into the input component's key handlers.
• src/tui/app.js:764-767 — Tab key toggles inputFocused. With ink-text-input, focus management may be handled by the component's built-in focus API, but the Tab key is consumed by Ink's raw mode at the process level, so App may still need to intercept Tab and call the component's focus methods.
• src/tui/inputPanel.js — The current InputPanel (Blink cursor component) would be replaced entirely. The cursor blinking behavior would be handled by ink-text-input natively.
• src/tui/app.js:741-752 — Onboarding input uses the same useInput pattern. This is a separate concern — onboarding may need its own input handling or a separate input component. The refactoring should keep onboarding isolated.
• src/tui/app.js:869-874 — InputPanel is rendered with inputText, cursorChar, and cursorColor props. These would change to value, onSubmit, and focus-related props.

[avoidwork]

Fixed in #592.