api(repos): Unbounded aggregate allocation in federated repository response

[euxaristia]

Summary

The anonymous endpoint GET /api/v1/repos/federated deserializes each reachable peer response into Vec<serde_json::Value> and accumulates rows without byte, row, or aggregate limits (crates/gitlawb-node/src/api/repos.rs:2945-2990).

Impact

A peer returning oversized JSON arrays causes unbounded heap retention and serialization work.

Remediation

1. Bound peer HTTP response bytes.
2. Cap rows per peer and aggregate total.
3. Deserialize bounded typed DTOs.

[beardthelion]

Partial overlap with #418: the unbounded peer read here is the api/repos.rs:2961 site already listed there. This issue adds the aggregate angle (per-peer row cap, total cap, typed DTOs) that a bounded body read alone does not cover, so keeping it open alongside #418. Retagged sev:medium to match the anonymous resource-exhaustion class (#164, #166, #263, #418); the fanout is an amplifier, not a new class.