Enable SGR mouse tracking and parse mouse escape sequences in the TUI input loop

[shouze]

Context

There's currently no mechanism to receive mouse events. The TUI reads raw stdin chunks as strings in for await (const chunk of process.stdin) (src/tui.ts) and matches them against known keyboard escape sequences. Mouse clicks/wheel arrive on this same channel as SGR sequences (\x1b[<b;x;yM / ...m) once mouse reporting is enabled on the terminal.

Part of #166.

Solution

• Enable mouse tracking (\x1b[?1000h\x1b[?1006h) on stdout when runInteractive() starts, next to the existing process.stdin.setRawMode(true).
• Disable it (\x1b[?1000l\x1b[?1006l) in every exit path — the exit() cleanup function, and any other place that calls setRawMode(false) — so a killed/crashed process never leaves the user's terminal stuck in mouse-reporting mode.
• Add a pure parser function (e.g. parseMouseEvent(sequence: string)) that recognizes SGR mouse sequences and returns a structured event ({ button, x, y, isRelease } or null for anything else). Place it in a new small module (e.g. src/render/mouse.ts or src/mouse.ts, to be decided based on whether it needs types.ts additions) so it can be unit-tested independently of the stdin loop.
• Wire the parser into the main input loop in tui.ts: unrecognized/malformed sequences are ignored (no throw), preserving graceful degradation for terminals without mouse support.

Acceptance Criteria

• Mouse tracking is active only while the TUI is running; verified that the terminal is not left in mouse-reporting mode after normal exit, Ctrl+C, and an unhandled error.
• A well-formed SGR mouse sequence is parsed into a structured event; malformed or unrelated sequences return null and are silently ignored (no crash, no visual glitch).
• Regular keyboard input continues to work unaffected (arrow keys, filter mode, etc. — full regression pass on existing shortcuts).

Definition of Done

• bun test passes, including a new companion *.test.ts for the parser covering: valid click press/release, valid wheel up/down, malformed sequence, empty string, partial/truncated sequence.
• bun run lint passes.
• bun run format:check passes.
• bun run knip passes (no unused exports/imports).
• bun run build.ts compiles successfully.
• No behavior change to existing keyboard shortcuts (manual regression check noted in the PR description).
• Documentation updated if this introduces any new observable behavior (e.g. a note that mouse reporting is enabled during interactive sessions).