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/internal/web/embed.go

@@ -4,3 +4,6 @@ import "embed"
 
 //go:embed templates/*
 var templateFS embed.FS
+
+//go:embed controller.yaml.default
+var defaultControllerTemplate string