Settings RPC replacing the v1 /config/* group, owning reload semantics #15328

Added by #15290 (not yet a row in the plan).

A settings RPC that replaces the v1 /config/* group and owns reload semantics. On v1, PATCH /config/overlay picks the target file by precedence and scope, checks a revision under a lock (409 on conflict), runs a shadow check (422 when a nearer file wins) and applies at once with no restart for console-only keys. None of that is in the v1 OpenAPI contract, and v2 reloads differently (debounced per-Location reload, no instance disposal), so the behavior needs an explicit RPC contract in the generated client.

Decision record: migration-tracking/plans/v2-plan-delta-2026-10-20.md (PR #15290).

First RPC in the RPC-then-TUI-then-VS-Code order (decision 16).