tui: keep key bindings discoverable in narrow terminals

[abhiksark]

Motivation

Keyboard actions continue to work in a narrow terminal, but the footer hides several essential bindings. A keyboard-only learner cannot discover topic navigation, documentation, or quit keys from the visible interface.

Current evidence

A 40 by 15 Textual pilot on dev at e1d4dae37234b75124bd6a53f06734296ebbbdee completed the full keyboard flow, but the track footer visibly stopped after F3:

visible: F1 Hint, F2 Reset, F3 List
clipped: F4 Topics, F5 Docs, Escape Quit, Ctrl+Q Quit

F4, F5, and Escape still executed correctly, so this is a responsive discoverability defect rather than broken key handling.

Exact scope

Provide a compact or otherwise accessible binding presentation when the footer cannot fit the normal labels. Keep the existing keys and actions unchanged.

Acceptance checklist

• A 40-column track screen exposes a discoverable route to F4, F5, and quit actions.
• Topic picker and documentation screens retain discoverable close or quit actions at the same size.
• The normal-width footer retains its current useful labels.
• Existing F1 through F5, Escape, and Ctrl+Q behavior is unchanged.
• A Textual pilot or snapshot test covers the narrow presentation.
• Keyboard-only navigation still completes the picker, track, docs, and exit flow.

Explicit exclusions

Do not change key assignments, remove footer help at normal widths, redesign the main three-pane layout, or add mouse-only controls.

Likely files

• pythonlings/screens/track.py
• pythonlings/screens/topic_picker.py
• pythonlings/screens/docs.py
• pythonlings/pythonlings.tcss
• tests/tui/test_app_pilot.py

Verification

python -m pytest tests/tui -q
python -m pytest -q
pythonlings --root tests/fixtures/passing_curriculum verify

Exercise the complete keyboard flow at 40 by 15 and at a normal terminal size.

Sprint coordination

See Discussion #37 and tracker #52. This issue is intentionally unassigned. A coordination comment is welcome, but it does not reserve the issue. The first pull request that satisfies every acceptance criterion and verification requirement is considered for merge.

[coderabbitai]

🔗 Related PRs

#31 - feat: overall progress, completion celebration, first-launch welcome (#14, #15, #16) [merged]

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[xjcway123]

I'd like to take this issue. I plan to add a compact, discoverable binding presentation for narrow terminals while preserving the existing key actions and normal-width footer. I'll also add TUI coverage for the 40×15 layout.