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/go.mod

@@ -16,7 +16,6 @@ require (
 	github.com/remyoudompheng/bigfft v0.0.0-20230129092748-24d4a6f8daec // indirect
 	golang.org/x/exp v0.0.0-20251023183803-a4bb9ffd2546 // indirect
 	golang.org/x/sys v0.37.0 // indirect
-	gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 // indirect
 	modernc.org/libc v1.67.6 // indirect
 	modernc.org/mathutil v1.7.1 // indirect
 	modernc.org/memory v1.11.0 // indirect