docs: update documentation to OKF v0.1 format

docs/database/challenges.md

@@ -3,7 +3,7 @@ type: database
 title: Challenge Tables
 description: category, challenge, challenge_file, and solve tables — how CTF challenges and scoring are stored.
 tags: [database, challenge, category, solve]
-timestamp: 2026-07-22T14:50:25Z
+timestamp: 2026-07-22T16:44:54Z
 ---
 
 # Tables
@@ -25,14 +25,19 @@ System rows are seeded by the
 `UpdateSystemCategoryKeys1700000000300` migration so the canonical
 keys are `CRY` (Cryptography), `MSC` (Misc), `PWN` (Binary
 exploitation), `REV` (Reverse Engineering), `WEB` (Web), and `HW`
-(Hardware). The migration drops any legacy seeded rows that no
-longer match the canonical set before inserting the missing entries.
+(Hardware). A forward-only repair migration,
+`RepairCategorySchemaAndSystemCategories1700000000400`, runs after
+that one on existing databases that pre-date the canonical six keys
+(it adds `created_at`/`updated_at` if missing, deletes obsolete
+`FOR`/`OSI` system rows, rewrites name/abbreviation/description/icon
+metadata on canonical rows, inserts any missing canonical row, and
+guarantees unique indexes on `system_key` and `abbreviation`).
 User-created categories leave `system_key` as `NULL`.
 
 The uniqueness on `abbreviation` is enforced both by application
 validation (uppercased on save, duplicates rejected) and by the
 `uq_category_abbreviation` index created in migration
-`1700000000200`.
+`1700000000200` (re-asserted by `1700000000400`).
 
 ## `challenge`