feat(journey): update_journey takes every setting REST does and answers what it replaced

The MCP tool lacked show_trip_tracks and cover_gradient, which PATCH
/api/journeys/:id has always taken. Both now read the input through one
helper, and the tool goes through a small settings service that writes the
same patch in a transaction with the stored values it replaces, answered
as previous, so a change can be written back. The subtitle and the cover
gradient take null to clear them. The tool's inline zod moves into strict
schemas in @trek/shared; the REST route and its body are unchanged.

server/scripts/mcp-inline-zod-baseline.json

@@ -14,7 +14,7 @@
     "src/nest/help/help.mcp.ts": 4,
     "src/nest/integrations/airtrail.mcp.ts": 2,
     "src/nest/integrations/dawarich.mcp.ts": 13,
-    "src/nest/journey/journey.mcp.ts": 57,
+    "src/nest/journey/journey.mcp.ts": 46,
     "src/nest/maps/maps.mcp.ts": 18,
     "src/nest/memories/memories.mcp.ts": 8,
     "src/nest/notifications/notifications.mcp.ts": 2,

server/scripts/size-baseline.json

@@ -11,7 +11,7 @@
   "src/nest/collections/collections.service.ts": 1478,
   "src/nest/doc-sync/doc-sync.service.ts": 1060,
   "src/nest/doc-sync/providers/synology-drive.client.ts": 1160,
-  "src/nest/journey/journey-domain.service.ts": 1770,
+  "src/nest/journey/journey-domain.service.ts": 1725,
   "src/nest/places/places.service.ts": 1592,
   "src/nest/plugins/plugin-runtime.service.ts": 1463,
   "src/nest/plugins/runtime/plugin-sdk.ts": 1093,