docs: update documentation to OKF v0.1 format

docs/database/schema.md

@@ -3,7 +3,7 @@ type: database
 title: Database Schema Overview
 description: SQLite (better-sqlite3) schema for HIPCTF: tables, relationships, indexes, and WAL journal mode.
 tags: [database, sqlite, typeorm, schema]
-timestamp: 2026-07-22T14:50:25Z
+timestamp: 2026-07-22T16:44:54Z
 ---
 
 # Overview
@@ -19,10 +19,15 @@ by a second migration
 (`backend/src/database/migrations/1700000000100-SeedSystemData.ts`).
 The initial migration declares every column used by the entities
 (including `category.created_at` and `category.updated_at`), so the
-later `AddCategoryTimestampsAndUniqueAbbrev1700000000200` and
-`UpdateSystemCategoryKeys1700000000300` migrations only patch legacy
-databases that pre-date those columns and reseed the canonical system
-rows.
+later `AddCategoryTimestampsAndUniqueAbbrev1700000000200`,
+`UpdateSystemCategoryKeys1700000000300`, and
+`RepairCategorySchemaAndSystemCategories1700000000400` migrations only
+patch legacy databases that pre-date those columns and reseed the
+canonical system rows. The `...0400` migration is idempotent and
+forward-only: it adds `created_at`/`updated_at` to legacy six-column
+`category` tables, deletes obsolete `FOR`/`OSI` system rows, rewrites
+metadata on canonical rows, inserts any missing canonical row, and
+re-asserts the unique indexes on `system_key` and `abbreviation`.
 
 # Tables