Fail loud when deploy --app matches nothing (#6)

## Summary

- Fail when `--app` / `--env` match no `host_apps` row (was silent no-op)
- Fail when `--app` missing from `app_catalog`

Prevents "deploy succeeded" that only refreshed web-static nginx while skipping Django — what happened on [chat_backend run 205](https://git.aimloperations.com/ai_ml_operations/chat_backend/actions/runs/205) before `chat_backend` was registered on master.

## Test plan

- [ ] `./scripts/deploy.sh --app does_not_exist --env prod` should fail with catalog message
- [ ] `./scripts/deploy.sh --app chat_backend --env prod` should proceed with Django once catalog/host_apps presentReviewed-on: #6

roles/app-deploy/tasks/main.yml

@@ -24,6 +24,29 @@
   ansible.builtin.debug:
     msg: "ref={{ app_ref | default('(per-app default branch)') }} targets={{ deploy_targets | map(attribute='name') | zip(deploy_targets | map(attribute='env')) | list }}"
 
+# Explicit --app/--env with no host_apps match used to silently no-op Django
+# and still refresh web-static (looked like a "static-only" deploy). Fail loud.
+- name: Fail when requested app+env is not on this host
+  ansible.builtin.fail:
+    msg: >-
+      No host_apps entry for app={{ app }} env={{ app_env }} on
+      {{ inventory_hostname }}. Check inventory/host_vars and app_catalog
+      (django apps need type: django + compose_file). Catalog keys:
+      {{ app_catalog.keys() | list }}.
+  when:
+    - app is defined
+    - app_env is defined
+    - deploy_targets | length == 0
+
+- name: Fail when requested app missing from app_catalog
+  ansible.builtin.fail:
+    msg: >-
+      app={{ app }} is not in app_catalog. Add it with type: django (docker)
+      or type: node-static. Known: {{ app_catalog.keys() | list }}.
+  when:
+    - app is defined
+    - app not in app_catalog
+
 - name: Deploy Django (docker compose) apps
   ansible.builtin.include_tasks: django.yml
   loop: "{{ deploy_targets | selectattr('name', 'in', django_names) | list }}"