feat(config): add tokenUrl, clientId, clientSecret to auth config (#17)

Closes homelab#12 (P3.7)

## Changes

- `AuthConfig`: added `TokenURL`, `ClientID`, `ClientSecret` fields
- `loader.go`: reads `tokenUrl`/`clientId` from YAML, `ClientSecret` from `AUTH_CLIENT_SECRET` env
- `deployment.yaml`: `AUTH_CLIENT_SECRET` from `api-gw-client-secret` Secret (optional)
- `gateway-config-secret.enc.yaml` + `configmap.yaml`: added `tokenUrl` and `clientId`

## Secret never in YAML

`clientSecret` deliberately omitted from YAML struct. Loaded from env only.

## Tests

3 tests: full config load, env-only secret, backward compat (missing fields = zero).

Co-authored-by: poimen <[email protected]>

internal/config/loader.go

@@ -25,6 +25,8 @@ type rawAuth struct {
 	Audience           string `yaml:"audience"`
 	JWKSURL            string `yaml:"jwksUrl"`
 	RequiredCapability string `yaml:"requiredCapability"`
+	TokenURL           string `yaml:"tokenUrl"`
+	ClientID           string `yaml:"clientId"`
 }
 
 // rawRoute represents a single route in the YAML configuration.
@@ -176,6 +178,9 @@ func LoadRoutesAndModelsFromFile(path string) (map[string]*Route, map[string]*Mo
 		Audience:           raw.Auth.Audience,
 		JWKSURL:            raw.Auth.JWKSURL,
 		RequiredCapability: raw.Auth.RequiredCapability,
+		TokenURL:           raw.Auth.TokenURL,
+		ClientID:           raw.Auth.ClientID,
+		ClientSecret:       os.Getenv("AUTH_CLIENT_SECRET"),
 	}
 
 	return routes, models, adapters, authConfig, nil