Add social post drafts and thumbnail

docs/launch/social-posts.md

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+# datasink launch posts
+
+Drafts for X and LinkedIn, written 8 October 2026. They have not been posted. Use `datasink-social-thumbnail.png` (1920×1080) as the image.
+
+Checked before writing: on 8 October 2026 the datasink.dev demo ran in a browser with no errors, and `npx datasink@0.4.1 scrub --demo` gave the same counts shown on the image (6 verified, 4 unverified, 2 invalid, 2 typos fixed). Without an AI key, `wash` skips the enrichment step with a clear message.
+
+## X
+
+I built datasink to clean up contact lists.
+
+It fixes email typos, checks each address has a working mail server, and merges duplicates. Your file stays in your browser.
+
+Free and open source.
+
+https://datasink.dev
+
+## LinkedIn
+
+I built a tool for cleaning up contact lists, and you can use it in your browser.
+
+It's called datasink. Drop in a CSV or spreadsheet and it fixes typos in email addresses, checks each one has a working mail server, and merges duplicates. Your file never leaves your machine. The only thing that goes out is each domain name, for the mail server check.
+
+If you'd rather work in the terminal, it's on npm: npx datasink demo runs the whole thing on sample data so you can see what it does first.
+
+It started out for music PR contact lists, and it works on any list of names and emails. Free and open source (MIT).
+
+https://datasink.dev