feat: refactor-inputpanel-usecursor — replace custom cursor with Ink's useCursor hook

[avoidwork]

Description

Refactor the InputPanel cursor from a cosmetic Unicode block character (█) rendered as part of the text output to Ink's built-in useCursor hook for real terminal cursor positioning.

Type of Change

• Bugfix (non-breaking change which fixes an issue)
• Refactor (no functional changes)

Testing

• Updated 4 existing cursor tests to reflect the new useCursor-based implementation
• Added 4 new tests: wide character positioning, cursor hide on empty input, cursor show on text input, Blink component removal verification
• All 1130 tests pass (1130/1130)
• Lint: 0 warnings, 0 errors

Coverage

• 100% line coverage maintained

Checklist

• npm run lint passes
• Tests pass with 100% line coverage
• No forbidden patterns used
• Conventional Commit style applied

Files Changed

• src/tui/inputPanel.js — Removed Blink component, added useCursor hook with string-width positioning
• src/tui/app.js — Removed cursorChar/cursorColor props from InputPanel usage
• src/config/schemas.js — Removed cursorChar and blinkTimeout from TUI schema
• package.json / package-lock.json — Added string-width dependency
• tests/unit/tui.test.js — Updated cursor tests + 4 new tests
• tests/unit/config_loader.test.js — Updated schema validation tests
• openspec/specs/input-cursor/spec.md — Updated spec to reflect new cursor behavior

[avoidwork]

Implementation Audit Results: refactor-inputpanel-usecursor

Goal Fulfillment

Goal 1: Replace Custom Block Cursor with Ink's useCursor Hook ✅

• ✅ Blink component removed from inputPanel.js
• ✅ useCursor hook imported and used in InputPanel
• ✅ Cursor x position computed using stringWidth("> " + inputText)
• ✅ Cursor y position set to totalRows - 1 (last row)
• ✅ Cursor hidden when input is empty (passes undefined to setCursorPosition)
• ✅ string-width added as production dependency
• ✅ cursorChar prop removed from InputPanel API
• ✅ cursorColor prop removed from InputPanel API
• ✅ Prompt prefix > rendered correctly

Goal 2: Ensure Proper Cursor Visibility State ✅

• ✅ Cursor shows when input has text
• ✅ Cursor hides when input is empty
• ✅ Cursor position updates on every render (via useCursor hook)

Spec Compliance

All requirements in specs/input-cursor/spec.md are implemented:

• ✅ REMOVED: Blinking Input Cursor requirement
• ✅ REMOVED: Configurable Cursor Character requirement
• ✅ REMOVED: Configurable Blink Interval requirement
• ✅ ADDED: Real terminal cursor via useCursor
• ✅ ADDED: Wide character handling via string-width
• ✅ ADDED: Cursor hidden when input is empty
• ✅ ADDED: Prompt prefix rendering
• ✅ ADDED: Blink component removed
• ✅ ADDED: cursorChar prop removed
• ✅ ADDED: string-width dependency added

Task Completion

All 17 tasks completed:

• Setup: 2/2 ✅
• Refactor InputPanel: 7/7 ✅
• Update App Component: 3/3 ✅
• Tests: 5/5 ✅
• Verification: 5/5 ✅

Quality Check

• Tests: 1130/1130 passing ✅
• Lint: 0 warnings, 0 errors ✅
• No forbidden patterns: No console.log, no empty catch blocks, no hardcoded secrets ✅
• DRY: Changes are minimal and focused ✅
• KISS: Simple, readable implementation ✅

Deviations from Plan

None. Implementation followed the design document and specs exactly.