feat(tui): add permission_prompt size options - #41978

Issue for this PR

Closes #28191

Type of change

• New feature

What does this PR do?

Adds two optional tui.json options to control the permission prompt panel:

• permission_prompt.max_height — max height of the panel when not fullscreen (defaults to 15, the previous hardcoded value).
• permission_prompt.default_expanded — open the permission prompt in fullscreen by default (false).

The height was previously hardcoded (maxHeight: 15) in packages/tui/src/routes/session/permission.tsx. When a large diff needs approval, 15 lines is often too small and users had to press ctrl+f every time. Both options are optional and backward-compatible: behavior is unchanged unless the user opts in.

Schema added in packages/tui/src/config/index.tsx following the existing prompt/cursor config patterns; default_expanded only takes effect when the prompt supports fullscreen (the main permission stage).

How did you verify your code works?

• Added config decode coverage in packages/tui/test/config.test.tsx (valid values pass, max_height: 0 throws).
• Ran bun test test/config.test.tsx in packages/tui — 9 pass.
• Ran bun typecheck from packages/tui and the full root bun typecheck — clean.

Screenshots / recordings

N/A (behavior only; no new UI surface).

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR