The OpenAPI document describes the fork tree: following, upstream, sync, make it yours and family #4871

Intent: a harness keeps a fork in step with its parent, or takes an app as its own, through OpenAPI alone.

Done:

• [ ] rows in src/contract/openapi.ts for GET {REPO}/following and {REPO}/following/proposals, the POST routes under {REPO}/following/ (converge, propose, propose-parent, sever, take), GET {REPO}/upstream with POST {REPO}/upstream/check, POST {REPO}/sync, {REPO}/make-it-yours and {REPO}/origin/reconnect, GET {REPO}/forks, GET {REPO}/tags, PATCH /api/v1/forge/following and GET /api/v1/family, placed right after the existing PATCH {REPO} (the repository settings row) row

Each row says what the route answers (the shape in its summary, exactly as the handler answers today), whether it needs a token (auth) and which scope, and its body fields, query and refusals, as the existing rows do. Use the methods src/http/api.ts registers. If a route needs "put" and #4844 has not yet added it to the Route method type, leave that route out and say so in the pull; do not add it here, because other issues would collide on that line. test/openapi.test.ts must still pass; add test/openapi-oa-fork.test.ts asserting each new path and method is in the served document. Other issues add rows in parallel, so put these exactly where named and nowhere else.