Add a 200ms click debounce with extensive behavioral tests

Per request: clicks of the same button closer together than
capture.clickDebounceMs (default 200ms) now collapse into a single step, so
accidental fast/double clicks don't each become a step. It is a leading-edge
debounce measured from the last *accepted* click, so a run of fast clicks
can't push the next deliberate click out — two clicks spaced beyond the
window (e.g. the reported 400-500ms apart) always register.

Replaces the prior 8ms duplicate-delivery suppression (subsumed by the
window). Configurable; 0 captures every click.

Tests (the point of this change is that it can't silently regress):
- 13 behavioral unit tests in capture.test.js that drive real onOsClick
  calls with controlled timestamps and assert which clicks survive — the
  reported 400/450/500ms cases, sub-window collapse, the 200ms boundary,
  per-button independence, configurability, debounce=0, last-accepted (not
  last-dropped) reference, session reset, and a full onOsClick -> queue ->
  store integration check. No keyword/comment assertions.
- A fourth end-to-end self-test scenario (burst of 40ms clicks collapses to
  1; three 300ms-apart clicks each register => 4 total). The marker/drain
  scenarios set debounce to 0 so they keep stressing the frame pipeline.

147 unit tests + all repo checks pass.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

core/settings.js

@@ -18,6 +18,11 @@ const DEFAULT_SETTINGS = {
     hotkeyPauseResume: 'CommandOrControl+Shift+2',
     captureOutsideClicks: true,
     confirmSimpleCapture: false,
+    // Leading-edge click debounce (ms): clicks of the same button closer
+    // together than this collapse into one step, so accidental fast/double
+    // clicks don't each become a step. Clicks spaced further apart always
+    // register. Set to 0 to capture every click.
+    clickDebounceMs: 200,
     autoIntervalSec: 5, // session fallback when click capture is unavailable
     // Strict click timing: a step never uses a frame whose grab started
     // after the click. Turn off only if captures are too slow to keep a