GET /api/v1/repos/:owner/:name/iterations carries an ETag and answers a repeat with 304 until a fork in the family moves #9223

The Iterations page and the MCP iterations tool re-read a whole fork family; while no fork moved, a repeat is a 304. The route already sets private, no-cache and vary but no validator.

Done looks like:

• [x] The /iterations route in src/http/api/iterations.ts answer 200 with a weak etag from weakEtag (src/http/etag.ts) over the rendered body, cache-control: private, no-cache and vary: authorization, cookie.
• [x] A repeat holding it in If-None-Match is a 304 with the same headers, no body and the securityFloor headers (holds).
• [x] The etag moves when a fork is made or deleted, a fork or the parent is pushed, or a fork turns private; two viewers shown different bodies never share an etag.
• [x] A missing repository (404) answer exactly as today, with no ETag, even with If-None-Match: *; the 304 is reached only after the access check.
• [x] test/iterations-etag.test.ts covers each of the above and fails without the change.

Files: src/http/api/iterations.ts, test/iterations-etag.test.ts. Risks: do not touch src/http/api.ts; bodies stay byte-for-byte as they are.

Reviewed pull #9228 at its head: ticked The /iterations route in src/http/api/iterations.ts answer 200 with a weak etag from weakEtag (src/http/etag.ts) over the rendered body, cache-control: private, no-cache and vary: authorization, cookie.; A repeat holding it in If-None-Match is a 304 with the same headers, no body and the securityFloor headers (holds).; The etag moves when a fork is made or deleted, a fork or the parent is pushed, or a fork turns private; two viewers shown different bodies never share an etag.; A missing repository (404) answer exactly as today, with no ETag, even with If-None-Match: *; the 304 is reached only after the access check.; test/iterations-etag.test.ts covers each of the above and fails without the change..