feat(db): add os_places to override_source enum

New provenance value for the deterministic OS Places classification-code
mapping written by the postcode-search journey (ADR-0007, on
feature/add-properties-by-postcode). Enum-only change so it can be
applied to the database ahead of the feature merging.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/app/db/migrations/0260_natural_enchantress.sql

@@ -0,0 +1 @@
+ALTER TYPE "public"."override_source" ADD VALUE 'os_places';

src/app/db/migrations/meta/_journal.json

@@ -1814,6 +1814,13 @@
       "when": 1783075096141,
       "tag": "0259_fantastic_rockslide",
       "breakpoints": true
+    },
+    {
+      "idx": 260,
+      "version": "7",
+      "when": 1783345567793,
+      "tag": "0260_natural_enchantress",
+      "breakpoints": true
     }
   ]
 }

src/app/db/schema/landlord_overrides.ts

@@ -262,6 +262,8 @@ export const MainHeatingSystemValues: [string, ...string[]] = [
 export const OverrideSourceValues: [string, ...string[]] = [
   "classifier",
   "user",
+  // Deterministic OS Places classification-code mapping (postcode search, ADR-0007)
+  "os_places",
 ];
 
 export const propertyTypeEnum = pgEnum("property_type", PropertyTypeValues);