fix: include migration files in @paperclipai/db and improve server error msg

- db build now copies src/migrations/ to dist/migrations/ after tsc,
  so SQL + meta JSON files are included in the published package.
  Without this, `import("@paperclipai/server")` fails at runtime with
  ENOENT when scanning for migration files.

- CLI's importServerEntry() now distinguishes between "module not found"
  and "server crashed during startup" for clearer error messages.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

packages/db/package.json

@@ -25,7 +25,7 @@
     "dist"
   ],
   "scripts": {
-    "build": "tsc",
+    "build": "tsc && cp -r src/migrations dist/migrations",
     "clean": "rm -rf dist",
     "typecheck": "tsc --noEmit",
     "generate": "tsc -p tsconfig.json && drizzle-kit generate",