Add tests/checks/test_click_capture_selftest.sh: runs the real Electron
STEPFORGE_CLICK_SELFTEST session and asserts every scenario passes — 3/3
markers at 0.00% offset, 8/8 burst clicks kept on finish, the first armed
click captured (warmup click ignored), and the debounce (4/4). Picked up
automatically by tests/run_test.sh. Skips cleanly when the host has no
capture environment so it never falsely fails CI, but fails the suite on any
real regression in click->screenshot->step behavior.
Document the guard in ARCHITECTURE.md and CHANGELOG.md.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>