chore: GitHub workflow revamp — GitHub Flow, community files, CI updates (#101)

* chore: add comprehensive .gitignore

* ci: update CI workflow for GitHub Flow

- Change triggers from develop to main (PRs to main + pushes to main)
- Add concurrency controls to cancel stale runs
- Update docker/build-push-action to v6
- Add descriptive job names for branch protection status checks
- Update screenshot refresh and docs sync to trigger on main pushes

* ci: update docker-publish for GitHub Flow

- Remove develop branch trigger (no more dev tag)
- Keep v* tag trigger for releases
- Update docker/build-push-action to v6

* docs: add community and governance files

- CONTRIBUTING.md with dev setup and PR guidelines
- SECURITY.md with vulnerability reporting policy
- CODE_OF_CONDUCT.md (Contributor Covenant v2.1 reference)
- PR template with conventional commits checklist
- Issue templates for bug reports and feature requests
- CODEOWNERS defaulting to @AnsoCode
- Dependabot config for npm (root, backend, frontend) and GitHub Actions

* docs: add README with badges, quick start, and contributing section

* chore: add LICENSE placeholder and open license decision issue (#100)

* docs: update CLAUDE.md for GitHub Flow branching model

- Replace develop-based Git Flow with GitHub Flow (main only)
- All branches now created off main, PRs target main
- Simplify release checklist (no develop-to-main merge step)
- Update testing strategy to reference Vitest and Playwright
- Fix docs.json reference (was mint.json)

* chore: track CLAUDE.md in version control

Remove CLAUDE.md from .gitignore so project workflow instructions
are versioned alongside the code they govern.

* docs: add MANUAL_STEPS.md for GitHub settings that require UI configuration

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,15 @@
+## What does this PR do?
+
+<!-- Brief description of the change -->
+
+## Related Issue
+
+<!-- Link to issue: Closes #123 -->
+
+## Checklist
+
+- [ ] Tests added/updated (if applicable)
+- [ ] Documentation updated (if applicable)
+- [ ] ESLint passes (`npm run lint` in backend/ and frontend/)
+- [ ] Commit messages follow Conventional Commits
+- [ ] CHANGELOG.md updated under `## [Unreleased]` (for user-facing changes)