Fix mobile file tab close spacing

[ymichael]

Human comments

What was wrong

File-preview tabs enlarge their close target to 36px on narrow coarse-pointer screens, but the selectable tab trigger retained its 6px desktop left inset. Centering the close glyph in that wider target moved it over the filename: the glyph ended at x=122 while the label began at x=120, producing a 2px overlap.

What changed

• Add a coarse-pointer left inset to non-icon tab triggers only when they have a close action with the enlarged touch target.
• Preserve the 36×36px close target while restoring 6px of visible space before the filename.
• Add focused regression coverage for the conditional file-tab spacing.
• No wire, CLI, guide, or documentation behavior changed.

How you verified

• Dev Browser at a 480×700 viewport with coarse-pointer emulation: the close-glyph-to-label gap changed from -2px to 6px while the close target remained 36×36px.
• The focused regression test failed before the fix and passed afterward.
• Post-rebase: pnpm exec turbo run test --filter=@bb/app --force -- --run src/components/ui/tab-pill.test.tsx (5 tests passed).
• Post-rebase: pnpm exec turbo run typecheck --filter=@bb/app --force.
• Full app verification before the no-op rebase: 456 test files passed, 3,643 tests passed, 4 skipped.

BB-Thread-ID: thr_q2ws2irggv

AGENT GENERATED