Exclude cancelled TODOs from checklist progress bar

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Summary

Fixes #2182

Cancelled inline checklist items (- [-]) were being counted toward the checklist progress bar's denominator, but never its numerator. This made tasks with cancelled TODO items appear less complete than they actually are.

Example from the issue: a task with one - [x] (completed) and one - [-] (cancelled) item showed 1/2 in the progress bar, when it should show 1/1 since the cancelled item shouldn't count at all.

Changes

• src/ui/taskCardProperties.ts: In calculateChecklistProgress, skip list items whose marker is - (cancelled) before incrementing total, so cancelled items are excluded from both the numerator and denominator.
• tests/unit/issues/issue-1576-display-progress-bar.test.ts:
  • Renamed/adjusted the existing "treats non-x task markers as incomplete" test to use a marker other than - (e.g. /), since - is no longer treated as merely "incomplete."
  • Added a test verifying cancelled (-) items are excluded from both numerator and denominator (1 done + 1 cancelled → 1/1, 100%).
  • Added a test verifying that when all items are cancelled, no progress bar is rendered (matches existing "no items" behavior).

Testing

• npx jest tests/unit/issues/issue-1576-display-progress-bar.test.ts — all 6 tests pass.
• Full test suite run: no new failures introduced (pre-existing unrelated failures are due to a generated src/releaseNotes.ts file not being present outside of the build process).
• npx eslint src/ui/taskCardProperties.ts --max-warnings=0 — clean.