Task: Replace Clerk (Replit-managed) with a standalone JWT/cookie-based auth system.
## What changed
### Backend (api-server)
- Added `admin_users` table (lib/db/src/schema/adminUsers.ts) with id, email (unique), password_hash, created_at; pushed to DB with drizzle-kit push
- Replaced `resolveAuth`/`requireAdmin` in auth.ts middleware: now reads a signed HS256 JWT from the `session` httpOnly cookie (via `jose`) instead of Clerk tokens
- Added `POST /api/auth/login` (bcrypt password check → sets httpOnly cookie), `POST /api/auth/logout` (clears cookie), `GET /api/me` (unchanged contract)
- Added `seedAdminUser()` in lib/seedAdmin.ts: on startup, if no admin exists, creates one from ADMIN_EMAIL + ADMIN_PASSWORD env vars (bcrypt-hashed)
- Removed all Clerk imports from app.ts: clerkMiddleware, publishableKeyFromHost, clerkProxyMiddleware deleted
- Deleted clerkProxyMiddleware.ts entirely
- Added cookie-parser middleware to app.ts
- Removed @clerk/express, @clerk/shared from package.json; added jose, bcryptjs, @types/bcryptjs
### Frontend (skillguard)
- Removed ClerkProvider, SignIn, SignUp, ClerkQueryClientCacheInvalidator from App.tsx; replaced with plain wouter routes
- Replaced /sign-in and /sign-up routes with a single /sign-in route pointing to new LoginPage
- New LoginPage (src/pages/login.tsx): email+password form using shadcn Input/Button/Card, calls POST /api/auth/login, redirects to /admin on success
- layout.tsx: replaced useClerk/useUser with useGetMe() + fetch POST /api/auth/logout
- require-admin.tsx: unchanged logic (already used useGetMe()), updated comment
- Removed @clerk/react, @clerk/localizations, @clerk/themes from package.json
- Added signInButton + loginError i18n keys to all 3 locales (de/en/es)
## New secrets required
- SESSION_SECRET (already existed)
- ADMIN_EMAIL (new — first admin email)
- ADMIN_PASSWORD (new — first admin password, stored as bcrypt hash)
## Removed env vars
- CLERK_SECRET_KEY, CLERK_PUBLISHABLE_KEY, VITE_CLERK_PUBLISHABLE_KEY, VITE_CLERK_PROXY_URL (can be deleted from secrets)
## Test results
All 79 tests pass.
Replit-Task-Id: 41d32d48-8f20-44bc-b665-a2becb83e503
441c828a17