ci: add ruff, pip-audit, CodeQL, and least-privilege permissions

[KristianP26]

Summary

Strengthens CI with linting/formatting, least-privilege permissions, supply-chain CVE scanning, and static security analysis.

Changes

• ruff — new ruff.toml (line-length 100, target-version py311). Fixed existing lint findings (unused imports; one load-bearing unused binding in main.py kept with # noqa: F841) and applied ruff format across the codebase. New lint job runs ruff check + ruff format --check.
• Least-privilege permissions — ci.yml now declares top-level permissions: contents: read; codeql.yml scopes its own.
• pip-audit — new audit job scans requirements.txt + requirements-build.txt for known CVEs (runs on Python 3.12 so the pyinstaller pin resolves). Currently clean.
• CodeQL — new codeql.yml running Python static analysis on push/PR to main and weekly.

Commits

Split into focused commits: ruff config → lint fixes → format → CI jobs → CodeQL → docs.

Verification

ruff check src/ tests/          # All checks passed!
ruff format --check src/ tests/ # already formatted
python -m unittest discover -s tests   # 36 passing

Note

The repo-wide ruff format commit will conflict with the open custom-hotkeys PR (#13), which rewrites several of the same files. Suggested order: merge #13 first, then rebase this branch and re-run ruff format.

ruff is pinned to 0.15.15 in the workflow; since it isn't a requirements manifest, Dependabot won't bump it — update manually when desired.

[github-advanced-security]

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[DavidHruby1]

Please rebase this onto current and resolve the conflicts before reopening. Also, this PR currently mixes CI/CD changes with Ruff/security code edits in src/ and tests/, so if the intent is to keep it as a pipeline PR, please split the non-CI changes out or confirm the bundled scope. Once it’s clean and up to date, I can merge it without touching the branch myself.

[DavidHruby1]

Please rebase this onto the current base branch and resolve the conflicts before reopening. Also, this PR currently mixes CI/CD changes with Ruff/security code edits in src/ and tests/, so if the intent is to keep it as a pipeline PR, please split the non-CI changes out or confirm the bundled scope. Once it’s clean and up to date, I can merge it without touching the branch myself.