Images, threads and the first two SDKs

New

• API: Upload an image with POST /media and get an id back.
• API: Attach an image to a post by id, with alt text.
• API: Images are delivered on X, LinkedIn and Bluesky.
• API: A post can carry a thread on X and Bluesky, or a first comment on LinkedIn, in the same request that sends it.
• SDKs: Node and Python SDKs are written by hand against the v2 API rather than generated, both versioned 2.0.0.
• SDKs: The Node and Python SDKs are written and merged, with npm and PyPI publishing next.
• SDKs: Until publishing lands the SDKs are not installable from a package registry, so the API itself is still the way in.
• Billing: Free accounts have one fair-use cap of 100 posts a day, counted in UTC across all your connections.
• Billing: Paid accounts have no daily cap.
• Billing: Sandbox posts never count toward the daily cap.