docs: remediate documentation gaps across quickstart, backup, config, API spec, and operations guides (#330)

- Fix Cyrillic character in quickstart image ref and correct registry to Docker Hub (saelix/sencho)
- Correct backup guide WAL references (Sencho uses SQLite default journal mode)
- Add SSL/TLS reverse proxy examples for Nginx, Traefik, and new Caddy configuration
- Add missing env vars (PORT, DATA_DIR, NODE_ENV, FRONTEND_URL, SSO_LDAP_DISPLAY_NAME) to .env.example
- Add upgrade & migration guide documenting automatic schema migrations
- Add self-hosting best practices (1:1 path rule, Docker socket security, resource recs)
- Add architecture overview (system design, request flow, database schema, multi-node model)
- Add development & contributor guide (setup, tests, code style, PR workflow)
- Update OpenAPI spec from v0.23.0 to v0.25.3 with Registries and Image Updates endpoints
- Update docs.json navigation with all new pages and API groups

.env.example

@@ -7,6 +7,18 @@ JWT_SECRET=your-secure-jwt-secret-here
 # Directory containing docker-compose files
 COMPOSE_DIR=/path/to/your/compose/files
 
+# HTTP server port (default: 3000)
+PORT=3000
+
+# Database and state directory inside the container (default: /app/data)
+DATA_DIR=/app/data
+
+# Node environment (set automatically in Docker image; only change for local dev)
+NODE_ENV=production
+
+# Frontend URL for CORS in production (leave empty for same-origin setups)
+FRONTEND_URL=
+
 # Global API rate limit (requests per minute per IP, production only)
 API_RATE_LIMIT=100
 
@@ -21,6 +33,7 @@ SSO_LDAP_SEARCH_BASE=ou=users,dc=example,dc=com
 SSO_LDAP_SEARCH_FILTER=(uid={{username}})
 SSO_LDAP_ADMIN_GROUP_DN=
 SSO_LDAP_DEFAULT_ROLE=viewer
+SSO_LDAP_DISPLAY_NAME=LDAP
 SSO_LDAP_TLS_REJECT_UNAUTHORIZED=true
 
 # Google OIDC