fix(migrate): support Supermemory v3 documents list API

[mgajewskik]

📋 Description

This PR fixes Supermemory -> OpenMemory migration failures caused by Supermemory API drift and hardens retry behavior in migration providers.

What changed

• Updated the Supermemory migration provider to use POST /v3/documents/list for connect/export.
• Updated pagination handling to current response fields (pagination.currentPage, pagination.totalPages).
• Added mapping support for current payload fields (createdAt, containerTags, customId).
• Replaced unbounded recursive 429 retry paths with bounded retry loops.
• Aligned the base provider export contract with async-generator usage in the migration runner.

Why this was necessary

• Previous Supermemory endpoint assumptions no longer matched current API behavior, causing migration connect/export failures.
• Current payload shape differs from older assumptions, leading to fragile transformations.
• Unbounded recursive retry behavior under sustained 429s could hang migration runs indefinitely.

🔄 Type of Change

• 🐛 Bug fix (non-breaking change which fixes an issue)
• ♻️ Code refactoring

🧪 Testing

• I have tested this change locally
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

Manual validation

• Verified migration CLI argument parsing with python -m tools.migrate --help.
• Verified Supermemory provider connection with a valid API key.
• Verified export iteration yields records using updated endpoint/pagination handling.

📚 Related Issues

Fixes Supermemory migration breakage due to API changes.

🚀 Deployment Notes

No runtime API/dashboard behavior changes. This PR only updates migration tooling.

[nullure]

LGTM