fix(Draggable): defer captureGesture to first motion (A22)

[re-marked]

Closes #72 (A22). Pairs with #81 (A21) to fully fix #55 (A3).

What

`MouseDownEvent` gains `captureGestureTentatively(handlers)`. Same first-call-wins rule as `captureGesture` (cross-protected — confirmed and tentative compete via the same single-slot field).

`Draggable` switches its press handler to `captureGestureTentatively`. App-level coordinator (`App.tsx`) gets `activeGestureTentative` flag and:

• Press: tentative capture installs the gesture but does NOT skip selection-start / multi-click bookkeeping.
• Motion: first motion promotes (cancels in-progress selection, clears tentative flag, fires onMove). After this point behaves identically to a confirmed capture.
• Release without motion: drops the gesture silently (no `onUp`) and falls through to normal release path → click dispatches to descendants normally.
• Lost-release recovery (focus-out, no-button-motion, fresh-press-while-active): tentative gestures drop silently; confirmed gestures still get `onUp` for cleanup.

Net effect

`I want clicks!` works on first try. No `stopImmediatePropagation` boilerplate. Same for `` / `` / any clickable child.

Test plan

• 708 tests passing (was 703; +5 for the new tentative API at the MouseDownEvent + dispatchMouseDown layers, plus updated Draggable assertion)
• typecheck / lint / build clean

API surface

• New: `MouseDownEvent.captureGestureTentatively(handlers)`, `MouseDownEvent.gestureTentative`
• Changed: `dispatchMouseDown` returns `CapturedGesture | null` (was `GestureHandlers | null`); same for `Ink.dispatchMouseDown` and `App.props.onMouseDownAt`. Tests updated.
• Existing `captureGesture` semantic unchanged — still confirmed-immediate, still first-call-wins.

Cross-refs

• A21: captureGesture last-call-wins inverts every other DOM "claim" semantic #71 (A21) — pairs with this for the full A3 fix
• A3: <Draggable> gesture capture eats onClick on inner children #55 (A3) — can be closed once A22 lands; the click-eating symptom is the union of A21 + A22
• A4: No window primitive — Draggable + Resizable don't compose #56 (A4 — Window primitive) — windows that contain interactive widgets directly benefit

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[chatgpt-codex-connector]

Reset click cadence when tentative capture becomes a drag

When a tentative Draggable press receives its first motion, it is now a real drag, but the press-time clickCount/lastClick* state that was updated below remains intact. After a small drag or trackpad jitter, a quick next click within the multi-click window and distance is treated as click #2 and goes through onMultiClick, suppressing the intended onClick; confirmed captures avoid this by resetting clickCount when they short-circuit. Clear the multi-click chain on promotion so promoted tentative drags behave like the existing captured-gesture path.

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