fix(tui): reuse stable native hyperlink identities

[daviddanialy]

Summary

• Emit stable OSC-8 IDs derived from the full clipped link span and a BLAKE3 digest of the escaped destination, using the existing dependency.
• Preserve main's single-pass rendering and unchanged-frame diff suppression. Partial text/style updates reuse the full link identity; separate spans and changed destinations remain distinct.
• Add regressions for partial styling, adjacent duplicate destinations, overlay restoration, clipping at nonzero viewport origins, skipped cells, wide-cell transitions, and bounded parameter-safe IDs. Update the UI overlay test for explicit IDs.

Why

VS Code freeze samples after closing a Kit terminal showed xterm spending time in clearAllMarkers / marker disposal. Anonymous OSC-8 openings allocate new markers when linked cells are repainted. Stable IDs allow xterm to reuse those link records instead of accumulating them on repeated diffs.

This complements the single-pass renderer from #228: unchanged frames already avoid output, but content/style changes within existing links still emit OSC-8 opens.

Review and validation

• Independent code review found no production correctness issues; strengthened coverage for the identified edge cases.
• mise run test -- --lib tui:: -- --test-threads=1 passed after the final review changes.
• mise run lint passed (format plus all-targets Clippy with all features and no default features).
• CLI and startup-picker integration suites passed: 13 tests.
• Fed actual renderer output into the installed VS Code xterm bundle: 10,000 partial redraws retained 3 markers, unchanged from the initial/warmed count. Verified destinations, overlay hide/restore, removal, and cursor position.

Existing validation limitations

The earlier full library run had 1,462 passes, 7 failures, and 5 ignored tests. Four failures passed on targeted retry. Two shell-output failures reproduce on the clean baseline because a local shell profile emits a missing-file warning into stderr. A Git credential/askpass test can stall on both baseline and patched builds; bounded retries were terminated. Parallel TUI signal-test interference also reproduces on the baseline, so the TUI suite was validated serially.

No claim of globally bounded marker storage for endlessly changing destinations or spans; this fixes repeated reuse of the same link. The separate Crossterm disconnect-loop issue is outside this PR.

[kit-code-agent]

No issues found. The changes look good to merge.