Add multi-user auth system and admin panel

- User model with email/hashed_password/is_admin/notification_prefs
- JWT auth: POST /api/auth/register, /login, /me
- First registered user auto-promoted to admin
- Migration 0005: users table + user_id FK on follows (clears global follows)
- Follows, dashboard, settings, admin endpoints all require authentication
- Admin endpoints (settings writes, celery triggers) require is_admin
- Frontend: login/register pages, Zustand auth store (localStorage persist)
- AuthGuard component gates all app routes, shows app shell only when authed
- Sidebar shows user email + logout; Admin nav link visible to admins only
- Admin panel (/settings): user list with delete + promote/demote, LLM config,
  data source settings, and manual celery controls

Authored-By: Jack Levy

backend/app/api/admin.py

@@ -1,35 +1,109 @@
-from fastapi import APIRouter
+from fastapi import APIRouter, Depends, HTTPException
+from sqlalchemy import func, select
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.core.dependencies import get_current_admin
+from app.database import get_db
+from app.models import Follow
+from app.models.user import User
+from app.schemas.schemas import UserResponse
 
 router = APIRouter()
 
 
+# ── User Management ───────────────────────────────────────────────────────────
+
+class UserWithStats(UserResponse):
+    follow_count: int
+
+
+@router.get("/users", response_model=list[UserWithStats])
+async def list_users(
+    db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(get_current_admin),
+):
+    """List all users with their follow counts."""
+    users_result = await db.execute(select(User).order_by(User.created_at))
+    users = users_result.scalars().all()
+
+    counts_result = await db.execute(
+        select(Follow.user_id, func.count(Follow.id).label("cnt"))
+        .group_by(Follow.user_id)
+    )
+    counts = {row.user_id: row.cnt for row in counts_result}
+
+    return [
+        UserWithStats(
+            id=u.id,
+            email=u.email,
+            is_admin=u.is_admin,
+            notification_prefs=u.notification_prefs or {},
+            created_at=u.created_at,
+            follow_count=counts.get(u.id, 0),
+        )
+        for u in users
+    ]
+
+
+@router.delete("/users/{user_id}", status_code=204)
+async def delete_user(
+    user_id: int,
+    db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(get_current_admin),
+):
+    """Delete a user account (cascades to their follows). Cannot delete yourself."""
+    if user_id == current_user.id:
+        raise HTTPException(status_code=400, detail="Cannot delete your own account")
+    user = await db.get(User, user_id)
+    if not user:
+        raise HTTPException(status_code=404, detail="User not found")
+    await db.delete(user)
+    await db.commit()
+
+
+@router.patch("/users/{user_id}/toggle-admin", response_model=UserResponse)
+async def toggle_admin(
+    user_id: int,
+    db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(get_current_admin),
+):
+    """Promote or demote a user's admin status."""
+    if user_id == current_user.id:
+        raise HTTPException(status_code=400, detail="Cannot change your own admin status")
+    user = await db.get(User, user_id)
+    if not user:
+        raise HTTPException(status_code=404, detail="User not found")
+    user.is_admin = not user.is_admin
+    await db.commit()
+    await db.refresh(user)
+    return user
+
+
+# ── Celery Tasks ──────────────────────────────────────────────────────────────
+
 @router.post("/trigger-poll")
-async def trigger_poll():
-    """Manually trigger a Congress.gov poll without waiting for the Beat schedule."""
+async def trigger_poll(current_user: User = Depends(get_current_admin)):
     from app.workers.congress_poller import poll_congress_bills
     task = poll_congress_bills.delay()
     return {"task_id": task.id, "status": "queued"}
 
 
 @router.post("/trigger-member-sync")
-async def trigger_member_sync():
-    """Manually trigger a member sync."""
+async def trigger_member_sync(current_user: User = Depends(get_current_admin)):
     from app.workers.congress_poller import sync_members
     task = sync_members.delay()
     return {"task_id": task.id, "status": "queued"}
 
 
 @router.post("/trigger-trend-scores")
-async def trigger_trend_scores():
-    """Manually trigger trend score calculation."""
+async def trigger_trend_scores(current_user: User = Depends(get_current_admin)):
     from app.workers.trend_scorer import calculate_all_trend_scores
     task = calculate_all_trend_scores.delay()
     return {"task_id": task.id, "status": "queued"}
 
 
 @router.get("/task-status/{task_id}")
-async def get_task_status(task_id: str):
-    """Check the status of an async task."""
+async def get_task_status(task_id: str, current_user: User = Depends(get_current_admin)):
     from app.workers.celery_app import celery_app
     result = celery_app.AsyncResult(task_id)
     return {