docs: ERC-4337 v0.7 migration guide + paymaster lifecycle (PR ready)

[enochTe8]

Hi ZeroDev team,

I'm Enoch, an ERC-4337 technical writer.

ZeroDev is one of the most powerful AA solutions in the ecosystem
— supporting both ERC-4337 and EIP-7702. Your docs deserve the
same depth.

I've identified two gaps I've already written fixes for:

• A v0.6 → v0.7 PackedUserOperation migration guide
• A paymaster lifecycle guide covering validate → execute → postOp
  with all failure modes and security patterns

I recently audited 8 production AA repositories and fixed three
critical technical bugs before delivery.

Everything is PR-ready: https://github.com/enochTe8

Happy to open the PR directly against this repo.

Best,
Enoch Agboola