feat: add ntn-compatible API parity command

[rossbrg]

Summary

• add an api <path> command with ntn-compatible inline body, query, header, stdin, JSON, multipart, method, and raw-response handling
• add compatibility aliases for login/logout, data sources, pages, and files
• add Notion token/version environment aliases plus per-request --notion-version
• embed an API endpoint catalog with ls, --spec, and --docs introspection
• document the new command and compatibility surface

Upstream sync

Rebased onto upstream main at e76dfa3. This deliberately leaves behind the fork commits already incorporated upstream by #90 and #107. Conflict resolution preserved the current workspace OAuth token masking and placed the API-parity entries under Unreleased.

Verification

• make fmt
• make test
• make build
• make lint
• live read-only ./build/notion-cli --auth-workspace haven api users/me --json
• ./build/notion-cli api ls --json

[rossbrg]

Closing this in favor of Notion's first-party ntn CLI. A current review found that the proposed parity surface now duplicates the actively maintained official CLI, while the static endpoint catalog is already stale and the raw absolute-URL path needs additional credential-safety work. My local workflows and workspace routing have been migrated to official ntn, so I no longer think this large compatibility layer should be merged.