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/bug_report.md

@@ -0,0 +1,47 @@
+---
+name: "\U0001F41B Bug report"
+about: Something isn't working as expected
+title: "[bug] "
+labels: bug
+assignees: ''
+---
+
+## Describe the bug
+
+A clear description of what the bug is.
+
+## Steps to reproduce
+
+1. Go to '...'
+2. Click on '...'
+3. See error
+
+## Expected behavior
+
+What you expected to happen.
+
+## Actual behavior
+
+What actually happened. Include screenshots if relevant.
+
+## Environment
+
+| Field | Value |
+|---|---|
+| immich-folio version | vX.X.X / commit SHA |
+| Immich version | |
+| Deployment | Docker / manual |
+| Browser | Chrome / Firefox / Safari |
+| OS | |
+
+## `content/gallery.yaml` (redacted)
+
+```yaml
+# Paste a minimal reproduction of your config here (remove any tokens/passwords!)
+```
+
+## Logs
+
+```
+# Paste relevant Docker / console logs here
+```