mobile: audit touch target sizes in bottom tabs

[duct-tape2]

Goal

Guarantee that all five bottom-navigation tabs expose a stable touch target of at least 48 logical pixels high. The target should remain large enough even if icon, font, or label metrics change later.

Where to work

• apps/mobile/App.tsx around the TABS.map(...) bottom-navigation buttons
• apps/mobile/scripts/verify-frontend-regressions.mjs for a focused regression guard

Suggested scope

1. Give each bottom-tab TouchableOpacity an explicit minHeight: 48 (or an equivalent stable layout rule) while preserving the five equal-width tabs.
2. Keep the existing hitSlop, accessibilityRole, accessibilityLabel, and selected accessibilityState behavior.
3. Extend the frontend regression script so removing the minimum target-size guarantee fails npm run verify.

Acceptance criteria

• Each of the five bottom tabs has a stable target height of at least 48 logical pixels.
• Labels and icons remain centered and do not overlap at narrow mobile width.
• Existing accessibility metadata remains intact.
• cd apps/mobile && npm run verify passes.
• python3 scripts/check_public_tree.py passes.
• The PR body includes Closes #13 and briefly explains the accessibility benefit.

Non-goals

• Do not replace the navigation architecture or redesign the tab bar.
• Do not add screenshots, generated assets, local engines, or private files.

Comment /claim before starting so another contributor is not assigned the same first issue.

[github-actions]

First PR recipe

Keep this to one useful change for this issue.

Inspect

• apps/mobile/App.tsx
• apps/mobile/scripts/verify-frontend-regressions.mjs

Done when

• Each of the five bottom tabs has a stable target height of at least 48 logical pixels.
• Labels and icons remain centered and do not overlap at narrow mobile width.
• Existing accessibility metadata remains intact.
• cd apps/mobile && npm run verify passes.
• python3 scripts/check_public_tree.py passes.
• The PR body includes Closes #13 and briefly explains the accessibility benefit.

Verify

• python3 scripts/check_public_tree.py
• cd apps/mobile && npm run verify
• python3 -m unittest discover -s scripts -p 'test_*.py'

Open the PR

• Write Closes #13 in the PR body.
• Say what changed and name the check or review you completed.
• Do not add generated media, archives, local engines, databases, secrets,
  screenshots, or private data.

Need a route?

• Browser edit: https://duct-tape2.github.io/ai-language-partner/community/FIVE_MINUTE_FIRST_PR.html
• Code or tests without local setup: https://duct-tape2.github.io/ai-language-partner/community/CODESPACES_FIRST_PR.html
• Ask a maintainer: First PR help desk: pick a useful starter issue #53