Preserve deferred chord handler when deduping duplicate key events (ChordHandler)

[SorraTheOrc]

When duplicate physical key events arrive while a chord pending-timer is active, the ChordHandler.feed() flow clears the existing timer and also clears pendingHandler. The duplicate dedupe branch then reschedules a timer but pendingHandler is null, which causes the deferred handler to be lost and never invoked.

This work item will:

• Update src/tui/chords.ts so clearing an existing timer does not drop a previously set pendingHandler; preserve/restore the handler across the dedupe path.
• Add a unit test to cover the scenario: a deferred single-key handler is pending, a duplicate physical event arrives, and after the timeout the deferred handler is invoked.

Acceptance criteria:

• ChordHandler.feed preserves deferred handlers when deduping duplicate events.
• New unit test in test/tui-chords.test.ts reproduces the issue and passes.
• All existing tests continue to pass.

Notes:

• Priority: medium.
• Issue discovered during PR review of PR Prevent intermittent TUI input stalls from chord pending state, opencode grabKeys leakage, and watcher refresh churn #930 (TUI freeze fixes).