M12b: category contract v2 on the server (schema 2, fourteen defaults, finer import mapping)

- migrations/0002_categories_v2.sql, byte-identical to contracts/schema/migrations/0002_categories_v2.sql
  (SPEC §14.1.1), with an identity test; SCHEMA_VERSION = 2 (E-1 reports it, the importer's check follows).
- Seed test on a fresh database (the fourteen rows of AC-7.2, server_version 11 to 14) and an upgrade test of a
  v1 database in use (0001 applied through the migrator, then users, a custom, a renamed and an archived default,
  an account, a recurring template, expenses): every earlier row unchanged, the four rows above the old
  sequence, foreign_key_check empty, schema_version 2, a pull from the old cursor returns exactly the four rows.
- DefaultCategoryKey with the fourteen keys (wire enum and contracts/openapi.yaml); icons 33 and colours 14
  (§9.7) in validation.
- The two category examples M12a held back (E-26 response-default, sync/pull-page-categories-v2) and its
  contracts-check patch for them and the enum.
- Importer: splitwise_categories.csv per the §10.8 v0.8 table (D-053), DEFAULT_KEYS of fourteen, synthetic
  fixtures for the finer mapping (Insurance/Försäkringar to insurance among them), a schema-1 refusal test.
- Test harnesses seed users at server_version 15/16 (after the fourteen seeds); pull counts 10 -> 14.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TQd3pEP9UeN2uifbHknQ7B

contracts/examples/sync/pull-page-categories-v2.json

@@ -0,0 +1,67 @@
+{
+  "epoch": "30b85fb529aac0016dc91650841005b9",
+  "since": 921,
+  "next_since": 925,
+  "has_more": false,
+  "server_time": "2026-10-25T12:00:05.000Z",
+  "users": [],
+  "categories": [
+    {
+      "id": "01920000-0000-7000-8000-000000000011",
+      "default_key": "housing",
+      "name": null,
+      "icon": "key",
+      "color": "indigo",
+      "sort_order": 25,
+      "created_at": "2026-10-18T00:00:00.000Z",
+      "updated_at": "2026-10-18T00:00:00.000Z",
+      "archived_at": null,
+      "deleted_at": null,
+      "server_version": 922
+    },
+    {
+      "id": "01920000-0000-7000-8000-000000000012",
+      "default_key": "insurance",
+      "name": null,
+      "icon": "shield",
+      "color": "slate",
+      "sort_order": 45,
+      "created_at": "2026-10-18T00:00:00.000Z",
+      "updated_at": "2026-10-18T00:00:00.000Z",
+      "archived_at": null,
+      "deleted_at": null,
+      "server_version": 923
+    },
+    {
+      "id": "01920000-0000-7000-8000-000000000013",
+      "default_key": "children",
+      "name": null,
+      "icon": "child_care",
+      "color": "lime",
+      "sort_order": 85,
+      "created_at": "2026-10-18T00:00:00.000Z",
+      "updated_at": "2026-10-18T00:00:00.000Z",
+      "archived_at": null,
+      "deleted_at": null,
+      "server_version": 924
+    },
+    {
+      "id": "01920000-0000-7000-8000-000000000014",
+      "default_key": "fees",
+      "name": null,
+      "icon": "account_balance",
+      "color": "amber",
+      "sort_order": 95,
+      "created_at": "2026-10-18T00:00:00.000Z",
+      "updated_at": "2026-10-18T00:00:00.000Z",
+      "archived_at": null,
+      "deleted_at": null,
+      "server_version": 925
+    }
+  ],
+  "accounts": [],
+  "recurring_templates": [],
+  "expenses": [],
+  "settlements": [],
+  "audit_entries": []
+}