[codex] add editor-compatible paid draft support

[nanameru]

Summary

• add editor-compatible paid draft save behavior using textContent body_length and paywall separator extraction
• add paid settings, separator candidates, magazine listing, and membership plan MCP tools
• migrate project Claude instructions and skills into Codex-facing AGENTS/.agents/.codex docs
• update docs and E2E image fixture for current note.com eyecatch ratio requirements

Validation

• uv run ruff check . && uv run ruff format --check . && uv run mypy .
• uv run pytest -q
• live draft verification: editor.note.com restored ProseMirror body and paywall line without publishing