Add user authentication with Supabase:
- Email/password signup
- Email/password login
- Password reset
- Session persistence (stay logged in)

User enters email + password
    ↓
App calls Supabase signUp()
    ↓
Supabase creates user
    ↓
(Optional) Email verification
    ↓
User is logged in

User enters email + password
    ↓
App calls Supabase signIn()
    ↓
Supabase validates credentials
    ↓
Session token returned
    ↓
User is logged in

Create a signup screen with:
- Email field with validation
- Password field (minimum 6 characters)
- Confirm password field
- "Create Account" button
- Link to "Already have an account? Log in"
- Show errors inline under fields

Create a login screen with:
- Email field
- Password field
- "Log In" button
- "Forgot Password?" link
- Link to "Don't have an account? Sign up"
- Show error message if login fails

Add a forgot password screen:
- Email field
- "Send Reset Link" button
- Success message after sending
- Link back to login

When the app starts, check if the user is logged in.
If logged in, go to the home screen.
If not logged in, show the login screen.

Show the current user's email on the profile screen

Add a sign out button that:
- Logs the user out of Supabase
- Returns to the login screen
- Clears local session data

After signup, show a message:
"Please check your email to verify your account"

When creating a new task, save the current user's ID with it
so each user only sees their own tasks.

-- Users can only see their own tasks
CREATE POLICY "Users see own tasks"
ON tasks FOR SELECT
USING (auth.uid() = user_id);

-- Users can only create tasks for themselves
CREATE POLICY "Users create own tasks"
ON tasks FOR INSERT
WITH CHECK (auth.uid() = user_id);

Handle authentication errors gracefully:
- Show specific error messages
- Don't reveal if email exists (security)
- Allow retry after errors