feat(6866): the proxy hop count is an admin setting, and the server shows what each count reads

An admin can save how many reverse proxies stand in front of Grimoire.
A saved count wins over TRUSTED_PROXY_HOPS, which stays the starting
value. Each worker loads it at startup (under a deadline) and re-reads
it every 30s; the worker that saves applies it at once.

GET/PUT /api/admin/proxy returns the count, where it came from, and a
readout of the admin's own request: the socket peer, the forwarding
chains, what counts 0-3 would read, and the count that reads
Cloudflare's visitor when Cloudflare's headers are present. Saves are
audit-logged. A "too many attempts" reply now says where to look when
everyone is being blocked.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/api-reference.md

@@ -281,6 +281,7 @@ These serve the plugin's hooks.
 | GET / PUT | `/api/admin/smtp` · POST `/api/admin/smtp/test` | SMTP config + test email |
 | GET | `/api/admin/logs` · `/api/admin/logs/stats` | Log entries + category counts |
 | GET / PUT | `/api/admin/base-url` | Get / set the public base URL |
+| GET / PUT | `/api/admin/proxy` | Get / set how many reverse proxies stand in front of Grimoire (`{"hops": n}`, or `null` for the environment's count), with what each count would read for this request |
 | GET / PUT | `/api/admin/db-maintenance` (+ `/health`, POST `/run`) | VACUUM schedule, health, manual run |
 | POST / GET / DELETE | `/api/admin/invitations` (+ `/:id`) | Create / list / revoke invite links |
 | GET / PUT | `/api/admin/backups` | Scheduled backups: destination, schedule and recent runs |