Anonymize sensitive information and add SSH setup documentation

Documentation:
- Add comprehensive SSH key setup guide in docs/SSH-SETUP.md
- Add SSH configuration sections to README.md and QUICKSTART.md
- Replace specific provider examples with generic alternatives
- Remove Hetzner/BorgBase specific instructions for broader applicability

Anonymization:
- Remove company/project specific names (Agence66 → generic)
- Generalize service names (/srv/app → /srv/*)
- Remove detailed application lists (/opt/nextcloud, etc. → /opt/*)
- Replace specific usernames and hostnames with placeholders
- Change repository label from 'serveur' to 'production'

Files updated:
- README.md: Add SSH setup, anonymize content
- QUICKSTART.md: Add SSH configuration steps
- CHANGELOG.md: Generalize paths list
- config.yaml: Generic title and label
- install.sh: Remove branding
- scripts/healthcheck.sh: Remove branding
- docs/SSH-SETUP.md: New comprehensive SSH guide

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

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

scripts/healthcheck.sh

@@ -24,7 +24,7 @@ ERRORS=0
 WARNINGS=0
 
 echo -e "${BLUE}==================================================${NC}"
-echo -e "${BLUE}Healthcheck Borgmatic - Agence66${NC}"
+echo -e "${BLUE}Healthcheck Borgmatic${NC}"
 echo -e "${BLUE}==================================================${NC}"
 echo ""