docs: log savedata corruption defense in CHANGELOG

Merge migrations 0007 and 0008 into a single 0007_savedata_integrity
migration since neither has been released yet.

server/migrations/sql/0007_savedata_integrity.sql

@@ -1,4 +1,6 @@
--- Rotating savedata backup table (3 slots per character, time-gated).
+-- Savedata integrity protections: rotating backups + checksum verification.
+
+-- Rotating backup table (3 slots per character, time-gated).
 -- Prevents permanent data loss from save corruption by keeping recent snapshots.
 CREATE TABLE IF NOT EXISTS savedata_backups (
     char_id     INTEGER NOT NULL REFERENCES characters(id) ON DELETE CASCADE,
@@ -7,3 +9,8 @@ CREATE TABLE IF NOT EXISTS savedata_backups (
     saved_at    TIMESTAMPTZ NOT NULL DEFAULT now(),
     PRIMARY KEY (char_id, slot)
 );
+
+-- SHA-256 checksum column for savedata integrity verification.
+-- Stored as 32 raw bytes (not hex). NULL means no hash computed yet
+-- (backwards-compatible with existing data).
+ALTER TABLE characters ADD COLUMN IF NOT EXISTS savedata_hash BYTEA;

server/migrations/sql/0008_savedata_hash.sql

@@ -1,4 +0,0 @@
--- Add SHA-256 checksum column for savedata integrity verification.
--- Stored as 32 raw bytes (not hex). NULL means no hash computed yet
--- (backwards-compatible with existing data).
-ALTER TABLE characters ADD COLUMN IF NOT EXISTS savedata_hash BYTEA;