Add lint job to CI and trigger on development branch

[crtahlin]

Sub-issue of #114 (developer experience review).

Task

Modify .github/workflows/ci.yml:

• Add lint job: checkout, Python 3.12, install ruff, run ruff check . and ruff format --check .
• Add development to push and pull_request branch triggers (currently only main)

Why

CI currently only runs tests — no style enforcement. PRs to development (the active branch) don't trigger CI at all. Adding both closes the gap.

[miles-on-nightshift]

Triage: classification: enhancement, priority: priority-medium

Linting in CI catches style issues before review. Low effort, high ongoing value.

[miles-on-nightshift]

Triage: feature / priority: low

CI lint job prevents formatting drift. Low urgency — no active contributors blocked.

Labels to add: enhancement, priority-low