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

server/crates/kvitt-server/migrations/0002_categories_v2.sql

@@ -0,0 +1,64 @@
+-- Kvitt server schema v2: four new default categories (housing, insurance, children, fees). Do not edit; add a new
+-- migration and bump the schema version (SPEC §14.8). Applied on top of server-v1.sql (0001_init.sql).
+--
+-- The default_key CHECK of categories cannot be altered in place in SQLite, so the table is rebuilt: copy the rows
+-- aside, drop the table, recreate it with the new CHECK and copy the rows back, ids and server_version unchanged.
+-- The migration runs inside one transaction (sqlx wraps every migration in one) with foreign_keys = ON (SPEC §8.9).
+-- defer_foreign_keys = ON lets expenses and recurring_templates point at categories while the table is briefly
+-- absent; the deferred check at commit still fails the migration if any reference is left dangling. It resets
+-- itself when the transaction ends. No other table, index or trigger refers to categories by anything but name.
+PRAGMA defer_foreign_keys = ON;
+
+CREATE TABLE categories_v1_copy AS SELECT * FROM categories;
+DROP TABLE categories;
+
+CREATE TABLE categories (
+    id             TEXT PRIMARY KEY NOT NULL,
+    default_key    TEXT UNIQUE CHECK (default_key IS NULL OR default_key IN
+                       ('groceries', 'restaurants', 'home', 'utilities', 'transport',
+                        'travel', 'entertainment', 'health', 'shopping', 'other',
+                        'housing', 'insurance', 'children', 'fees')),
+    name           TEXT CHECK (name IS NULL OR length(name) BETWEEN 1 AND 40),
+    icon           TEXT NOT NULL,
+    color          TEXT NOT NULL,
+    sort_order     INTEGER NOT NULL,
+    created_at     TEXT NOT NULL,
+    updated_at     TEXT NOT NULL,
+    archived_at    TEXT,
+    deleted_at     TEXT,
+    server_version INTEGER NOT NULL UNIQUE,
+    CHECK (name IS NOT NULL OR default_key IS NOT NULL)
+) STRICT;
+
+INSERT INTO categories (id, default_key, name, icon, color, sort_order, created_at, updated_at, archived_at, deleted_at, server_version)
+    SELECT id, default_key, name, icon, color, sort_order, created_at, updated_at, archived_at, deleted_at, server_version
+    FROM categories_v1_copy;
+DROP TABLE categories_v1_copy;
+
+-- Each new row takes the next server_version from the global sequence, as every server write does (SPEC §14.1), so
+-- phones receive the rows on their next pull whatever their cursor.
+UPDATE sync_sequence SET value = value + 1 WHERE id = 1;
+INSERT INTO categories (id, default_key, name, icon, color, sort_order, created_at, updated_at, archived_at, deleted_at, server_version)
+    SELECT '01920000-0000-7000-8000-000000000011', 'housing', NULL, 'key', 'indigo', 25,
+           '2026-10-18T00:00:00.000Z', '2026-10-18T00:00:00.000Z', NULL, NULL, value
+    FROM sync_sequence WHERE id = 1;
+
+UPDATE sync_sequence SET value = value + 1 WHERE id = 1;
+INSERT INTO categories (id, default_key, name, icon, color, sort_order, created_at, updated_at, archived_at, deleted_at, server_version)
+    SELECT '01920000-0000-7000-8000-000000000012', 'insurance', NULL, 'shield', 'slate', 45,
+           '2026-10-18T00:00:00.000Z', '2026-10-18T00:00:00.000Z', NULL, NULL, value
+    FROM sync_sequence WHERE id = 1;
+
+UPDATE sync_sequence SET value = value + 1 WHERE id = 1;
+INSERT INTO categories (id, default_key, name, icon, color, sort_order, created_at, updated_at, archived_at, deleted_at, server_version)
+    SELECT '01920000-0000-7000-8000-000000000013', 'children', NULL, 'child_care', 'lime', 85,
+           '2026-10-18T00:00:00.000Z', '2026-10-18T00:00:00.000Z', NULL, NULL, value
+    FROM sync_sequence WHERE id = 1;
+
+UPDATE sync_sequence SET value = value + 1 WHERE id = 1;
+INSERT INTO categories (id, default_key, name, icon, color, sort_order, created_at, updated_at, archived_at, deleted_at, server_version)
+    SELECT '01920000-0000-7000-8000-000000000014', 'fees', NULL, 'account_balance', 'amber', 95,
+           '2026-10-18T00:00:00.000Z', '2026-10-18T00:00:00.000Z', NULL, NULL, value
+    FROM sync_sequence WHERE id = 1;
+
+UPDATE meta SET value = '2' WHERE key = 'schema_version';