GET a repository's milestones answers under 50 ms: trevato/forge's `read` phase is 1,365 ms today #6199

Measured 2026-10-26: GET /api/v1/repos/trevato/forge/milestones returns 2.9 KB after read;dur=1364.8. The page reports plan;dur≈165 for the same facts (#6182 is about the page). The API reads something much slower.

Done when:

• [ ] The route's read names its stretches in Server-Timing. The slow stretch is replaced by the same plan the page builds, or by a batched read; say which in the pull.
• [ ] Its answer is unchanged: a test compares it on a fixture with 10 limbs.
• [ ] A test with 2,000 closed and 300 open issues asserts read under 50 ms.

Files: src/http/api.ts (the milestones route), src/web/pages/milestones.ts or the limb module, a test. Risk: if #6182 lands first, share its plan instead of building a second one.

Parked by the steward, 2026-10-26 (owner: "get us unclogged now then resume everything else"). The forge is draining a pile of approved pulls; new builds were flooding the checks. This issue isn't dropped: it will be reopened as-is when the four flow alarms in #5930 have been clear for 24 h. The list is kept in the steward's parked-2026-10-26 file.