Fix ActivateJailDialog blocking logic and mypy false positive

Two frontend bugs and one mypy false positive fixed:

- ActivateJailDialog: Activate button was never disabled when
  blockingIssues.length > 0 (missing condition in disabled prop).
- ActivateJailDialog: handleConfirm called onActivated() even when
  the backend returned active=false (blocked activation). Dialog now
  stays open and shows result.message instead.
- config.py: Settings() call flagged by mypy --strict because
  pydantic-settings loads required fields from env vars at runtime;
  suppressed with a targeted type: ignore[call-arg] comment.

Tests: added ActivateJailDialog.test.tsx (5 tests covering button state,
backend-rejection handling, success path, and crash detection callback).

backend/app/config.py

@@ -85,4 +85,4 @@ def get_settings() -> Settings:
         A validated :class:`Settings` object. Raises :class:`pydantic.ValidationError`
         if required keys are absent or values fail validation.
     """
-    return Settings()
+    return Settings()  # type: ignore[call-arg]  # pydantic-settings populates required fields from env vars