refactor: Co-locate server artifacts under apps/server/

Move drizzle/, dist/, and coverage/ into apps/server/ so all
server-specific artifacts live alongside the source they belong to.

- git mv drizzle/ → apps/server/drizzle/
- drizzle.config.ts: out → ./apps/server/drizzle
- tsconfig.json: outDir → ./apps/server/dist, exclude drizzle dir
- package.json: main/bin/clean point to apps/server/dist/
- vitest.config.ts: reportsDirectory → ./apps/server/coverage
- .gitignore: add coverage/ entry
- ensure-schema.ts: update getMigrationsPath() for new layout
- docs/database-migrations.md: update drizzle/ references

apps/server/db/ensure-schema.ts

@@ -20,10 +20,10 @@ const log = createModuleLogger('db');
  */
 function getMigrationsPath(): string {
   const currentDir = dirname(fileURLToPath(import.meta.url));
-  // In dev (tsx): apps/server/db/ — need 3 levels up to workspace root
-  // In dist (tsc): dist/db/ — need 2 levels up to workspace root
-  const upThree = join(currentDir, '..', '..', '..', 'drizzle');
-  if (existsSync(upThree)) return upThree;
+  // Dev: apps/server/db/ → 1 up → apps/server/drizzle/
+  // Dist: apps/server/dist/db/ → 2 up → apps/server/drizzle/
+  const upOne = join(currentDir, '..', 'drizzle');
+  if (existsSync(upOne)) return upOne;
   return join(currentDir, '..', '..', 'drizzle');
 }