fix(bounty-details): polish mobile responsiveness across header, tabs, conversation and submissions

[syndrome4002-leo]

Summary

• IssueDetailsPage: tabs now use variant="scrollable" with mobile-tuned font/padding/minWidth; outer container uses tighter px and Stack spacing on xs, and the watchlist star sits closer to the header card on small screens.
• IssueHeaderCard:
  • Responsive card padding (p: { xs: 2, md: 3 }), title shrinks to 1.15rem on xs with wordBreak: 'break-word', repo link wraps long org/repo names.
  • Meta row redesigned: on mobile a 2-column grid with Bounty | Author on row 1 and Created spanning full-width on row 2 (with subtle top/bottom borders so it reads as a stat strip); on desktop a flex row with vertical 1px dividers between cells.
  • All cells top-aligned (alignItems: 'flex-start') so the BOUNTY / AUTHOR / CREATED labels share the same baseline regardless of cell height.
  • Author truncates with ellipsis, Created date locked to one line.
• IssueConversation: avatar drops to 32×32 on xs (was 40), gap and header padding/font tighten, the speech-bubble pointer arrow is hidden on xs (it added noise next to the smaller avatar), header wraps cleanly when the username line overflows.
• IssueSubmissionsTable: responsive header padding, PR title cells wrapped in Tooltip so the full title is visible on hover when truncated, Date column locked to one line, table keeps minWidth: 640 so columns retain readable widths and scroll horizontally on narrow viewports.

Test plan

• Open /bounties/details?id=31 at desktop width (≥md) — header, tabs, conversation and submissions should look identical to before this PR.
• Resize to ~768px (sm) — tabs collapse, header card padding tightens but layout stays single-row.
• Resize to mobile (375px / iPhone SE) — verify:
  • BOUNTY + AUTHOR sit side-by-side; CREATED on its own line below; all three labels at same vertical position.
  • Title wraps cleanly inside the card.
  • Watchlist star sits flush to the right of the header card.
  • Conversation avatar is smaller, no speech-bubble arrow.
  • Submissions tab: PR title hover shows full title in tooltip; dates do not break across two lines; horizontal scroll engages cleanly.
• Stress-test at 320px width (smallest common phone) — nothing overflows the card.
• Long author logins on the header card truncate with ellipsis instead of pushing the layout.

Related Issues

Close: #939

Type of Change

• Bug fix
• New feature
• Refactor
• Documentation
• Other (describe below)

Screenshots

Before:

bandicam.2026-05-04.21-03-12-379.mp4

Now:

bandicam.2026-05-04.21-06-49-141.mp4

Before:

bandicam.2026-05-04.21-04-29-812.mp4

Now:

bandicam.2026-05-04.21-05-39-642.mp4

Before:

Now:

Before:

Now:

Checklist

• New components are modularized/separated where sensible
• Uses predefined theme (e.g. no hardcoded colors)
• Responsive/mobile checked
• Tested against the test API
• npm run format and npm run lint:fix have been run
• npm run build passes
• Screenshots included for any UI/visual changes

[anderdc]

Fix conflicts.

[syndrome4002-leo]

@anderdc I just fixed conflicts, Could you please review again?