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

package.json

@@ -7,14 +7,14 @@
     "apps/*",
     "packages/*"
   ],
-  "main": "./dist/index.js",
+  "main": "./apps/server/dist/index.js",
   "bin": {
-    "cw": "./dist/bin/cw.js"
+    "cw": "./apps/server/dist/bin/cw.js"
   },
   "scripts": {
     "build": "tsc",
     "dev": "tsx watch apps/server/bin/cw.ts",
-    "clean": "rimraf dist",
+    "clean": "rimraf apps/server/dist",
     "test": "vitest run",
     "test:watch": "vitest",
     "test:coverage": "vitest run --coverage",