feat: replace profiles with kubernetes-style secrets

Replace the confused Profile abstraction with a dedicated Secret resource
following Kubernetes conventions. Servers now have env entries with inline
values or secretRef references. Env vars are resolved and passed to
containers at startup (fixes existing gap).

- Add Secret CRUD (model, repo, service, routes, CLI commands)
- Server env: {name, value} or {name, valueFrom: {secretRef: {name, key}}}
- Add env-resolver utility shared by instance startup and config generation
- Remove all profile-related code (models, services, routes, CLI, tests)
- Update backup/restore for secrets instead of profiles
- describe secret masks values by default, --show-values to reveal

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

src/mcpd/src/routes/backup.ts

@@ -13,7 +13,7 @@ export function registerBackupRoutes(app: FastifyInstance, deps: BackupDeps): vo
   app.post<{
     Body: {
       password?: string;
-      resources?: Array<'servers' | 'profiles' | 'projects'>;
+      resources?: Array<'servers' | 'secrets' | 'projects'>;
     };
   }>('/api/v1/backup', async (request) => {
     const opts: BackupOptions = {};
@@ -51,7 +51,7 @@ export function registerBackupRoutes(app: FastifyInstance, deps: BackupDeps): vo
 
     const result = await deps.restoreService.restore(bundle, restoreOpts);
 
-    if (result.errors.length > 0 && result.serversCreated === 0 && result.profilesCreated === 0 && result.projectsCreated === 0) {
+    if (result.errors.length > 0 && result.serversCreated === 0 && result.secretsCreated === 0 && result.projectsCreated === 0) {
       reply.code(422);
     }