Split the TUI root component into focused modules

[TheGreatAxios]

Summary

Splits src/tui/app.tsx into focused sibling hooks under src/tui/hooks/, along the seams: layout/scroll geometry, message pipeline, quota retry, image attach, command context, and drain logic (plus a provider-auth hook for Codex/xAI login and re-auth handling). This is pure code motion — no logic changes, no behavior changes.

New files:

• src/tui/hooks/use-quota-retry.ts
• src/tui/hooks/use-image-attach.ts
• src/tui/hooks/use-drain-logic.ts
• src/tui/hooks/use-message-pipeline.ts
• src/tui/hooks/use-command-context.ts
• src/tui/hooks/use-transcript-layout.ts
• src/tui/hooks/use-provider-auth.ts

src/tui/app.tsx drops from 2409 to 1766 lines. src/tui/runner.tsx (including the CycleTextRecorder dispose/reset wiring) is untouched.

Closes CL-4364

Verification

• bun run typecheck — passes
• bun run build — passes
• bun test — 3565 pass, 0 fail, across 274 files (full suite, including the previously-flaky tests/unit/tui/{app,use-scroll,onboarding,use-gates} suites, run both individually and as part of the full suite)

[linear-code]

CL-4364