GRM-22: Add developer documentation and update project configuration

- Add CONTRIBUTING.md with branch naming, commit format, and PR workflow
- Add TROUBLESHOOTING.md with common issues and solutions
- Update README.md with CI badge and commit convention section
- Update pyproject.toml with pythonpath and coverage settings for scripts

CONTRIBUTING.md

@@ -0,0 +1,54 @@
+# Contributing to GRM
+
+Thank you for contributing to Gitea Runner Manager (GRM)!
+
+## Branch Naming
+
+All feature branches **must** include a `GRM-N` prefix corresponding to the Vikunja task identifier. Examples:
+
+- `GRM-19`
+- `GRM-19-fix-bug`
+- `GRM-42-add-update-command`
+
+The `GRM-N` prefix is mandatory — CI extracts it for merge messages and Vikunja updates.
+
+## Commit Format
+
+Use **conventional commits** on feature branches:
+
+```
+feat: add new command
+fix: resolve timeout issue
+chore: update dependencies
+docs: improve README
+```
+
+Allowed types: `feat`, `fix`, `chore`, `docs`, `style`, `refactor`, `perf`, `test`, `ci`, `build`, `revert`, `BREAKING CHANGE`.
+
+**Do NOT** include the `GRM-N:` prefix in commit messages on feature branches — it is added automatically during squash merge.
+
+## PR Workflow
+
+1. Create a branch `GRM-N` or `GRM-N-brief-description` from `master`
+2. Make changes, committing with conventional format
+3. Push and open a PR against `master`
+4. CI runs lint, unit tests, and molecule tests
+5. When all checks pass, add the `ready-to-merge` label
+6. The auto-merge workflow squash-merges with message `GRM-N: <PR title>`
+7. The post-merge workflow updates the Vikunja task
+
+## Local Testing
+
+```bash
+make test-all    # Runs pytest-cov + molecule
+make lint-all    # Runs ruff, pyright, ansible-lint, checkmake
+make pytest-cov  # Unit tests with 100% coverage enforcement
+make molecule    # All 7 molecule scenarios
+```
+
+## Code Quality
+
+- **ruff**: Line length 120
+- **pyright**: Strict mode
+- **Test coverage**: 100% required
+- **ansible-lint**: For all Ansible content