[codex] Fix short-window layout overflow

[jiaxindeyang-a11y]

Summary

• Let the sidebar and chat pane scroll vertically when the desktop window is shorter than the fixed chrome/footer stack.
• Change the status bar from clipping overflow to horizontal scrolling so right-side metrics remain reachable in windowed layouts.
• Update the typography overflow contract test to lock in the new behavior.

Root Cause

The desktop shell used fixed-height chrome/footer regions inside a body/layout that hides overflow. At very short heights, content outside the available column height was clipped. The status bar also forced a single line while using overflow: hidden, so metrics at the right edge disappeared when the window was not wide enough.

Validation

• npm.cmd run check:css
• npx.cmd tsx src/__tests__/typography-overflow-contract.test.ts
• npm.cmd test
• npm.cmd run test:typecheck was attempted but still fails locally because desktop/frontend/wailsjs is not generated in this checkout (Cannot find module '../../wailsjs/go/main/App').
• Vite served http://127.0.0.1:5174/ with HTTP 200, but screenshot-level Browser verification was blocked by the local Windows sandbox (CreateProcessAsUserW failed: 5).