feat: add Gitea self-hosted Git service with Actions runner

- Create new 'dev' stack at dev.pivoine.art
- Add Gitea with PostgreSQL database (core stack)
- Add Gitea Actions runner with Docker support
- Enable mailer configuration via SMTP
- Enable container registry and packages
- Add gitea database to PostgreSQL init script

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

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

core/postgres/init/01-init-databases.sh

@@ -41,6 +41,10 @@ psql -v ON_ERROR_STOP=1 --username "$POSTGRES_USER" --dbname "$POSTGRES_DB" <<-E
     SELECT 'CREATE DATABASE asciinema'
     WHERE NOT EXISTS (SELECT FROM pg_database WHERE datname = 'asciinema')\\gexec
 
+    -- Gitea self-hosted Git service database
+    SELECT 'CREATE DATABASE gitea'
+    WHERE NOT EXISTS (SELECT FROM pg_database WHERE datname = 'gitea')\\gexec
+
     -- Grant privileges to all databases
     GRANT ALL PRIVILEGES ON DATABASE directus TO $POSTGRES_USER;
     GRANT ALL PRIVILEGES ON DATABASE umami TO $POSTGRES_USER;