fix(renderer): make gesture capture leaf-first

[re-marked]

Summary

• make MouseDownEvent.captureGesture(...) first-call-wins instead of last-call-wins
• stop onMouseDown bubbling once a descendant captures the gesture, preventing ancestor Draggable wrappers from stealing it
• add dispatcher and Draggable regression coverage plus docs/changelog updates for the new leaf-first contract

Notes

This closes the A21 semantic bug. It also improves the A3 workaround shape: a child inside <Draggable> can now claim a press with captureGesture without also calling stopImmediatePropagation().

Plain onClick inside an eagerly-capturing <Draggable> still needs A22's deferred-capture work before A3 can be fully closed.

Verification

• pnpm test -- packages/renderer/src/events/mouse-event.test.ts packages/renderer/src/components/Draggable.test.tsx
• pnpm --filter @yokai-tui/renderer typecheck
• pnpm --filter @yokai-tui/renderer lint
• pnpm test
• pnpm --filter @yokai-tui/renderer build
• git diff --check

Closes #71
Refs #55
Refs #72