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>

src/grimoire/routes/auth.py

@@ -9,7 +9,7 @@ from quart import Blueprint, g, jsonify, redirect, request, session
 from grimoire.auth import login_required, get_current_user_id
 from grimoire.config import Config
 from grimoire.proxy import client_ip
-from grimoire.rate_limit import is_rate_limited
+from grimoire.rate_limit import SHARED_ADDRESS_HINT, is_rate_limited
 from grimoire.services.auth import (
     authenticate,
     change_password,
@@ -49,7 +49,7 @@ async def register():
     if not Config.LOCAL_AUTH_ENABLED:
         return jsonify({"error": "Local authentication is disabled. Please use SSO."}), 403
     if await is_rate_limited(f"register:{client_ip()}", max_requests=5, window_seconds=300):
-        return jsonify({"error": "Too many registration attempts. Try again later."}), 429
+        return jsonify({"error": f"Too many registration attempts. Try again later. {SHARED_ADDRESS_HINT}"}), 429
     if not await is_registration_open():
         return jsonify({"error": "Registration is closed"}), 403
 
@@ -79,7 +79,7 @@ async def login():
     if not Config.LOCAL_AUTH_ENABLED:
         return jsonify({"error": "Local authentication is disabled. Please use SSO."}), 403
     if await is_rate_limited(f"login:{client_ip()}", max_requests=10, window_seconds=60):
-        return jsonify({"error": "Too many login attempts. Try again later."}), 429
+        return jsonify({"error": f"Too many login attempts. Try again later. {SHARED_ADDRESS_HINT}"}), 429
     data = await request.get_json()
     username = (data.get("username") or "").strip()
     password = data.get("password") or ""
@@ -235,7 +235,7 @@ async def forgot_password():
 @auth_bp.route("/reset-password", methods=["POST"])
 async def reset_password():
     if await is_rate_limited(f"reset:{client_ip()}", max_requests=10, window_seconds=60):
-        return jsonify({"error": "Too many attempts. Try again later."}), 429
+        return jsonify({"error": f"Too many attempts. Try again later. {SHARED_ADDRESS_HINT}"}), 429
     data = await request.get_json()
     token = (data.get("token") or "").strip()
     new_password = data.get("new_password") or ""