v0.27.0:0 - in-app settings gear + swap-lock route fix

Move the ~20 optional cluster knobs out of the StartOS "Configure Sparks"
action (now just the 4 required fields) and into a dashboard ⚙ Settings gear,
backed by a /data/app_settings.json overlay keyed by env-var names. One shared
mutable Settings instance + Settings.reload() applies edits live without a
restart; existing installs' values migrate automatically on first boot.

Also: support-service ports (parakeet/kokoro/embed/qdrant + vllm) are now
configurable, and GET /api/swap/lock no longer 404s (it was shadowed by the
/api/swap/{job_id} catch-all). WebhookNotifier is re-pointed on save so its
url/secret reload live too.

image/tests/conftest.py

@@ -15,3 +15,6 @@ sys.path.insert(0, str(Path(__file__).resolve().parent.parent))
 os.environ.setdefault("REDACTION_MAP_DB", "/tmp/spark_control_test_maps.db")
 os.environ.setdefault("CONNECTIVITY_LOG", "/tmp/spark_control_test_connectivity.json")
 os.environ.setdefault("MODELS_OVERRIDES", "/tmp/spark_control_test_overrides.yaml")
+# Keep the in-app settings overlay off the container-only /data path; tests that
+# care about its contents point it at their own tmp file via monkeypatch.
+os.environ.setdefault("APP_SETTINGS_FILE", "/tmp/spark_control_test_app_settings.json")