fix(data): restore hierarchical fields in district metadata

Re-added system/station/district fields to district.yaml that were
incorrectly removed during Tyre10 cleanup. These carry hierarchical
context (planet, station), not redundant identity. Made canonical_id
optional in schema since it's derived from directory path at load time.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

content/_schema/district.schema.json

@@ -4,13 +4,13 @@
   "title": "District Metadata",
   "description": "District definition file — one per district directory (D-036).",
   "type": "object",
-  "required": ["canonical_id", "display_name", "system", "station", "district", "description", "locations", "npc_count"],
+  "required": ["display_name", "system", "station", "district", "description", "locations", "npc_count"],
   "additionalProperties": false,
   "properties": {
     "canonical_id": {
       "type": "string",
       "pattern": "^[a-z]+\\.[a-z]+\\.[a-z-]+$",
-      "description": "Canonical ID in format {system}.{station}.{district}"
+      "description": "Optional — derived from directory path at load time. If present, must match {system}.{station}.{district}."
     },
     "display_name": {
       "type": "string",

content/districts/sova-transit/district.yaml

@@ -1,5 +1,6 @@
 # Sova Transit District metadata (D-036)
-canonical_id: "krenn.sova.transit"
+# Source of truth for identity: directory path (districts/sova-transit/).
+# canonical_id is derived from the path at load time by ContentValidator.
 display_name: "Sova Transit District"
 system: "krenn"
 station: "sova"