Add admin panel with member management and password reset

Features:
- Admin panel at /settings/members for workspace owners
- View all workspace members with roles and last login
- Create new users directly (with temporary password)
- Change member roles (Owner/Editor/Viewer)
- Reset user passwords (forces change on next login)
- Remove members from workspace
- Force password reset flow on login
- Track last login timestamp for users

API Routes:
- GET/POST /api/workspaces/[id]/members
- GET/PATCH/DELETE /api/workspaces/[id]/members/[memberId]
- POST /api/workspaces/[id]/members/[memberId]/reset-password
- POST /api/auth/change-password

Schema changes:
- Added lastLoginAt DateTime? to User model
- Added forcePasswordReset Boolean to User model

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

prisma/schema.prisma

@@ -12,12 +12,14 @@ datasource db {
 // ============================================
 
 model User {
-  id           String   @id @default(cuid())
-  email        String   @unique
-  passwordHash String
-  name         String
-  createdAt    DateTime @default(now())
-  updatedAt    DateTime @updatedAt
+  id                 String    @id @default(cuid())
+  email              String    @unique
+  passwordHash       String
+  name               String
+  createdAt          DateTime  @default(now())
+  updatedAt          DateTime  @updatedAt
+  lastLoginAt        DateTime?
+  forcePasswordReset Boolean   @default(false)
 
   // Relations
   sessions           Session[]