feat: customer config management — CRUD, API retrieval, per-customer auth (v0.2.0)

New "Configurations" section lets operators pre-configure customer settings
in the Hub, then docker-setup.sh can download a ready-made controller.yaml
using just a customer ID and retrieval password.

- Store: customer_configs table with CRUD + per-customer API key lookup
- API: GET /api/v1/config/{id} with X-Retrieval-Password auth
- Auth: per-customer API keys alongside existing global key (backward compatible)
- Web UI: /configs list, create, edit, delete, YAML preview, copy-to-clipboard
- YAML gen: deep-merge controller.yaml.example template with customer overrides
- Template fetcher: background goroutine refreshing template from Gitea repo
- Navigation: Dashboard / Configurations tabs on all pages

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

hub/configs/hub.yaml.example

@@ -31,6 +31,14 @@ retention:
 alerting:
   stale_threshold: "30m"     # Customer considered stale if no report for this duration
 
+# --- Registry / template fetching ---
+registry:
+  image: "gitea.dooplex.hu/admin/felhom-controller"
+  username: ""               # Gitea username (for version check + template fetch)
+  token: ""                  # Gitea token
+  check_interval: "6h"      # How often to check for new controller versions
+  template_interval: "1h"   # How often to fetch controller.yaml.example for config generation
+
 # --- Server ---
 server:
   listen: ":8080"