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).

frontend/src/components/config/ActivateJailDialog.tsx

@@ -152,6 +152,13 @@ export function ActivateJailDialog({
 
     activateJail(jail.name, overrides)
       .then((result) => {
+        if (!result.active) {
+          // Backend rejected the activation (e.g. missing logpath or filter).
+          // Show the server's message and keep the dialog open so the user
+          // can read the explanation without the dialog disappearing.
+          setError(result.message);
+          return;
+        }
         if (result.validation_warnings.length > 0) {
           setValidationWarnings(result.validation_warnings);
         }
@@ -336,7 +343,7 @@ export function ActivateJailDialog({
             <Button
               appearance="primary"
               onClick={handleConfirm}
-              disabled={submitting || validating}
+              disabled={submitting || validating || blockingIssues.length > 0}
               icon={submitting ? <Spinner size="tiny" /> : undefined}
             >
               {submitting ? "Activating and verifying…" : "Activate"}