Challenge: Build the Increment

Add an increment instruction to the counter program.

Requirements

1. Add a pub fn increment inside the #[program] module
2. It should take ctx: Context<Increment> and return Result<()>
3. Get a mutable reference to ctx.accounts.counter and add 1 to count
4. Add an Increment accounts struct with counter (PDA, mut, same seeds as Initialize) and user (Signer)

Why user is needed in Increment

The counter is a PDA derived from [b"counter", user.key()]. To verify the PDA matches, Anchor needs the user account to re-derive the seeds. This also acts as authorization — only the wallet that matches the seeds can modify this counter.

Tips

• The Increment struct needs the <'info> lifetime, just like Initialize
• The counter field needs seeds and bump (same seeds as Initialize, but no init)
• The user field is Signer<'info> (not mut — they don't pay anything here)
• Don't change the existing initialize or greet instructions