Document v0.1 scope and integration stubs

[jmcte]

Summary

• document the fixture-mode v0.1 scope and explicitly call out live adapter/live export stubs
• add live MailPlus adapter and live export integration guides for Phase 2 contributors
• add Keep-a-Changelog release notes and versioning policy
• expose mailplus_intelligence.__version__ from package metadata
• link release-v0.1 / Phase 2 tracking from README and AGENTS

Verification

• PYTHONPATH=src python3.12 -m unittest discover -s tests -p 'test_runtime.py' -v
• bash scripts/ci/run-fast-checks.sh

Closes #85.

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 834af0ae43

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".

[chatgpt-codex-connector]

Update SyncBatch example to avoid invalid next_cursor arg

The worked IMAP stub currently constructs SyncBatch with next_cursor, but SyncBatch only defines source_name, cursor, and messages in src/mailplus_intelligence/sync.py (SyncBatch dataclass). Anyone implementing Phase 2 by following this guide will hit TypeError: __init__() got an unexpected keyword argument 'next_cursor' at runtime, so the integration instructions are not executable as written.

Useful? React with 👍 / 👎.