feat(services): env doctor — surface empty vars, bad refs, unreadable secrets

GET /services/:id/env-check (read scope) reports, without exposing values:
- unresolved: ${{service.KEY}} refs that don't match a sibling service/env
- empty: variables with blank values
- unreadable: secrets whose ciphertext fails decryption (key rotation)

install.sh now generates SECRETS_KEY explicitly (was falling back to
JWT_SECRET — a rotation would orphan ciphertext). .env.example documents it.

Surfaces: CLI `services env-check`, MCP containr_services_env_check
(90 tools), OpenAPI path, and a warning banner in the service Variables
panel listing each issue.

Verified live: injected a bogus ${{nosuchservice.PORT}} var plus an
unreadable ciphertext row; the endpoint flagged both, ok=false.

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

app/frontend/src/lib/api-client.ts

@@ -1304,6 +1304,17 @@ export const restartService = (serviceId: string) => serviceAction(serviceId, 'r
 export const sleepService = (serviceId: string) => serviceAction(serviceId, 'sleep');
 export const wakeService = (serviceId: string) => serviceAction(serviceId, 'wake');
 
+export type EnvCheckResult = {
+  ok: boolean;
+  unresolved?: string[];
+  empty?: string[];
+  unreadable?: string[];
+};
+
+export async function getServiceEnvCheck(serviceId: string): Promise<EnvCheckResult> {
+  return requestJson<EnvCheckResult>(`/services/${serviceId}/env-check`);
+}
+
 export async function redeployService(serviceId: string): Promise<ServiceRuntime> {
   const payload = await requestJson<{ runtime?: ServiceRuntime }>(`/services/${serviceId}/redeploy`, {
     method: 'POST',