chore: remove unused packages, imports, and stale type definitions

- Remove @casl/prisma (unused) from backend
- Remove @heroicons/react (unused, using lucide-react) from frontend
- Remove unused InferSubjects import from ability.factory.ts
- Remove unused Calendar import from Dashboard.tsx
- Delete stale frontend/src/lib/types.ts (duplicate of src/types/index.ts)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/package-lock.json

@@ -11,7 +11,6 @@
         "@auth0/auth0-react": "^2.2.4",
         "@casl/ability": "^6.8.0",
         "@casl/react": "^5.0.1",
-        "@heroicons/react": "^2.2.0",
         "@react-pdf/renderer": "^4.3.2",
         "@tanstack/react-query": "^5.17.19",
         "axios": "^1.6.5",
@@ -912,15 +911,6 @@
         "node": "^12.22.0 || ^14.17.0 || >=16.0.0"
       }
     },
-    "node_modules/@heroicons/react": {
-      "version": "2.2.0",
-      "resolved": "https://registry.npmjs.org/@heroicons/react/-/react-2.2.0.tgz",
-      "integrity": "sha512-LMcepvRaS9LYHJGsF0zzmgKCUim/X3N/DQKc4jepAXJ7l8QxJ1PmxJzqplF2Z3FE4PqBAIGyJAQ/w4B5dsqbtQ==",
-      "license": "MIT",
-      "peerDependencies": {
-        "react": ">= 16 || ^19.0.0-rc"
-      }
-    },
     "node_modules/@humanwhocodes/config-array": {
       "version": "0.13.0",
       "resolved": "https://registry.npmjs.org/@humanwhocodes/config-array/-/config-array-0.13.0.tgz",