chore: add GitHub community files and CI pipeline

- .github/workflows/ci.yml: TypeScript check + Vitest + build on every PR
- .github/dependabot.yml: weekly npm + Actions updates (minor/patch grouped)
- .github/ISSUE_TEMPLATE/: bug_report, feature_request, config (→ Discussions)
- .github/PULL_REQUEST_TEMPLATE.md: checklist for contributors
- SECURITY.md: responsible disclosure policy via GitHub Advisories
- CONTRIBUTING.md: dev setup, code style, commit conventions

.github/ISSUE_TEMPLATE/feature_request.md

@@ -0,0 +1,27 @@
+---
+name: "\U0001F4A1 Feature request"
+about: Suggest an idea or improvement
+title: "[feat] "
+labels: enhancement
+assignees: ''
+---
+
+## Summary
+
+A brief description of the feature you'd like to see.
+
+## Problem / motivation
+
+What problem does this solve? Is it connected to a specific workflow?
+
+## Proposed solution
+
+Describe the solution you'd like.
+
+## Alternatives considered
+
+Any alternative approaches you've thought about?
+
+## Additional context
+
+Screenshots, mockups, links to similar implementations, etc.