feat: add Linkwarden bookmark manager stack

Added new Links stack to Falcon infrastructure:

**Links Stack (links.pivoine.art):**
- Linkwarden bookmark manager with PostgreSQL backend
- Meilisearch v1.12.8 for full-text search
- Browser extension support
- Screenshot and PDF archiving
- Collaborative bookmark sharing

**Infrastructure Updates:**
- Created links/compose.yaml with linkwarden and meilisearch services
- Added linkwarden database to PostgreSQL init script
- Added LINKS_* environment variables to arty.yml
- Updated compose.yaml to include links stack
- Cleaned up .env to contain only secrets
- Added all EMAIL_* variables to .env

**Documentation:**
- Updated CLAUDE.md with Links service details
- Updated README.md with Links in CORE SYSTEMS table
- Added linkwarden_data and meili_data volumes to docs

**Required Secrets (in .env):**
- LINKS_NEXTAUTH_SECRET: NextAuth.js session encryption
- LINKS_MEILI_MASTER_KEY: Meilisearch API authentication

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

compose.yaml

@@ -7,6 +7,7 @@ include:
   - scrapy/compose.yaml
   - n8n/compose.yaml
   - stash/compose.yaml
+  - links/compose.yaml
   - umami/compose.yaml
   - proxy/compose.yaml
   - watch/compose.yaml