fix(frontend): restore member self-assignment for shifts and tasks

Root Cause:
- Shift: Next.js 16.1.6 incompatible rewrite pattern caused runtime SyntaxError
- Task: Missing self-assignment UI for member role

Fix:
- Updated next.config.ts rewrite pattern from regex to wildcard syntax
- Added "Assign to Me" button to task detail page with useSession integration
- Added test coverage for self-assignment behavior with session mocks

Testing:
- Lint: ✅ PASS (ESLint v9)
- Tests: ✅ 47/47 PASS (Vitest v4.0.18)
- Build: ✅ PASS (Next.js 16.1.6, 12 routes)

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-opencode)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

frontend/package.json

@@ -16,6 +16,7 @@
     "@tanstack/react-query": "^5.90.21",
     "class-variance-authority": "^0.7.1",
     "clsx": "^2.1.1",
+    "jsdom": "^28.1.0",
     "lucide-react": "^0.576.0",
     "next": "16.1.6",
     "next-auth": "^5.0.0-beta.30",