fix(tui): restore reliable mouse and responsive layout

[t41372]

Summary

• require a semantic primary press and matching release, cancel stale owners, and route pointer input to the topmost visible overlay
• make responsive root, body, footer, picker, modal, and management geometry usable at exact and zero-size boundaries
• keep Unicode grapheme, tab, selection, and caret behavior correct while bounding multiline rendering to the visible viewport, including content beyond 65,535 rows
• make terminal redraws selective and verify real SGR mouse input through a final-grid PTY oracle

Validation

• cargo fmt --all --check
• cargo clippy --locked --workspace --all-targets --all-features -- -D warnings
• RUSTDOCFLAGS="-D warnings" cargo doc --locked --workspace --all-features --no-deps
• fresh isolated workspace tests/examples plus every benchmark under aggregate LLVM coverage
• bash scripts/check_coverage.sh /tmp/skit-tui-mouse-pr-final-v2.lcov — complete executable-source line coverage
• survivor-driven mutation scans, exact current reruns, and line-level fault injection for the final overlay and viewport changes
• cargo deny --locked check, cargo audit --deny warnings, Zizmor, and the documentation type/build/link checks

Scope

The UI model walker is intentionally not included here. PR #48 remains separate and untouched.

[coderabbitai]

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[codecov]

Codecov Report

❌ Patch coverage is 99.95448% with 3 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
crates/skit-tui/src/terminal.rs	99.56%	2 Missing ⚠️
crates/skit-tui/src/pointer.rs	99.73%	1 Missing ⚠️

📢 Thoughts on this report? Let us know!

[codspeed-hq]

Merging this PR will not alter performance

✅ 23 untouched benchmarks
⏩ 20 skipped benchmarks¹

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_{Comparing fix/tui-mouse (0edf38c) with rewrite/rust-ratatui-complete-20260808-codex (5af68f8)}

Footnotes

1. 20 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩