v0.12.1 — every endpoint routes in fleet serve

Completes the multi-project serve story from v0.12.0: in a bare tesserae serve (every registered project), all /api/* now route to the right project — /api/ask, /api/ask/health, /api/transcript-search by the page's /<alias>/ Referer, and /api/clip (which comes from an external page) by an explicit project alias in the body, the sole registered project, or a 400 listing the aliases. The Chrome extension gained a Target project setting. Transcript search fails closed with 409 when two projects share a directory name (memex can't scope them apart). Plus docs: a compile --extractor guide and cognee GRAPH_COMPLETION / fleet live-ask coverage. Drop-in over v0.12.0.

Full notes: https://github.com/ca1773130n/Tesserae/blob/main/docs/release-notes/v0.12.1.md