feat(api): add hp_regen_since column for persistent HP regeneration

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

apps/api/src/database/migrations/1792000000000-AddHpRegeneration.ts

@@ -0,0 +1,25 @@
+import { MigrationInterface, QueryRunner } from 'typeorm';
+
+export class AddHpRegeneration1792000000000 implements MigrationInterface {
+  public async up(queryRunner: QueryRunner): Promise<void> {
+    await queryRunner.query(
+      'ALTER TABLE "characters" ADD COLUMN "hp_regen_since" TIMESTAMP WITH TIME ZONE',
+    );
+
+    // Existing characters start regenerating immediately from their current
+    // HP. A character whose fight is still ACTIVE keeps regeneration paused
+    // until that fight resolves, matching the "no combat-time regen" rule
+    // (persistent-hp-and-regeneration design, R4) -- this migration must not
+    // gift them free healing mid-fight.
+    await queryRunner.query('UPDATE "characters" SET "hp_regen_since" = now()');
+    await queryRunner.query(`UPDATE "characters" AS "character"
+      SET "hp_regen_since" = NULL
+      FROM "combats" AS "combat"
+      WHERE "combat"."character_id" = "character"."id"
+        AND "combat"."status" = 'ACTIVE'`);
+  }
+
+  public async down(queryRunner: QueryRunner): Promise<void> {
+    await queryRunner.query('ALTER TABLE "characters" DROP COLUMN "hp_regen_since"');
+  }
+}

apps/api/src/database/migrations/add-hp-regeneration.migration.spec.ts

@@ -0,0 +1,17 @@
+import 'reflect-metadata';
+import { getMetadataArgsStorage } from 'typeorm';
+import { Character } from '../../characters/entities/character.entity';
+
+describe('characters.hp_regen_since schema', () => {
+  it('stores the regeneration anchor as a nullable timestamptz', () => {
+    const metadata = getMetadataArgsStorage();
+    const column = metadata.columns.find(
+      (candidate) =>
+        candidate.target === Character && candidate.propertyName === 'hpRegenSince',
+    );
+
+    expect(column).toBeDefined();
+    expect(column?.options.type).toBe('timestamptz');
+    expect(column?.options.nullable).toBe(true);
+  });
+});