Refactor create-agent-dialog: extract hook and type select

[selfcontained]

Summary

• Extracted use-create-agent-form.ts (377 lines) — all form state, effects, callbacks, and the submit handler moved into a custom hook
• Extracted agent-type-select.tsx (119 lines) — self-contained agent type dropdown combobox with its own open/close state management
• create-agent-dialog.tsx reduced from 760 → 357 lines, now a thin render shell

Why this was a candidate

The create-agent dialog had 760 lines with 15+ useState hooks, 6 useEffect hooks, 9 useCallback handlers, and a complex submit handler — all mixed with a two-step form JSX. The hook extraction separates logic from presentation; the type select extracts a self-contained UI widget.

New file structure

create-agent-dialog.tsx          357 lines  (was 760) — render shell
use-create-agent-form.ts         377 lines  (new)     — form logic hook
agent-type-select.tsx            119 lines  (new)     — type dropdown
create-agent-dialog-utils.ts     (unchanged)          — prefs, cwd history
create-agent-dialog-clipboard.ts (unchanged)          — clipboard helpers
create-agent-worktree-section.tsx (unchanged)          — worktree UI

Next run

The next componentizer run will tackle feedback-panel.tsx (660 lines).

Test plan

• pnpm run finalize:web — type check + production build pass
• pnpm run test:e2e — all 172 tests pass (12 terminal-live skipped as expected)
• Pre-commit hooks (prettier, eslint, tsc) pass

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