fix: force interactive login shell for bash containers

Detached containers with tty: true still exited immediately because a
plain /bin/bash invocation exits with code 0 when stdin is not connected.

- Detect when the container CMD is /bin/bash or bash and exec an
  interactive login shell () after dropping privileges
- Keep the generic  path for non-shell commands
- Bump compiler_version to v4 to force a fresh image build

Quality gates:
- pytest tests/unit: 219 passed
- ruff: clean on changed files
- mypy: clean on changed files

apps/api/tests/.pi-map.index.md

@@ -2,7 +2,7 @@
 dir: apps/api/tests
 
 ## role
-Provides shared test infrastructure and fixtures for API integration testing
+Provides shared test infrastructure and fixtures for the API application's test suite.
 ## parent
 index: apps/api/.pi-map.index.md
 map: apps/api/.pi-map.md