fix(sessions): render string tool inputs as multiline content

[KinomotoMio]

Summary

• render top-level string tool inputs with the existing multiline content viewer
• keep object-valued generic tool inputs on the existing field-grid path
• add regression coverage for Codex apply_patch, HTML escaping, and object fallback behavior

Scope

This is intentionally limited to the Sessions presentation layer. Codex parsing, persistence, raw input display, and renderer styles are unchanged.

Verification

• node --experimental-test-module-mocks --test tests/app-tool-renderer.test.mjs (11 passed)
• npm test (277 passed)
• npm run typecheck
• npm run lint (0 errors; 4 pre-existing warnings)
• cd app && npx electron-vite build
• real captured apply_patch input: 6,878 characters / 412 lines rendered as 1 content block and 0 character field rows

Closes #11