Phase 5: [link account linking

BridgeAccountLink ties a game account to a website account. [link mints a
one-time, 5-minute code from an unambiguous alphabet (no O/0/I/1), holds it in a
Core-thread dict keyed to the account, and emits link.request. The website
relays the code back through the sidecar as link.confirm; the shard validates,
writes the WebsiteUserId account tag, and replies link.ok. A bad or expired code
gets link.error.

The tag persists to accounts.xml in ServUO's standard <tags> format, read by
LoadTags at boot, so a link survives restarts with no new persistence layer.
mob.login now carries webId when the account is linked, so the sidecar can
attribute a session to a site user without a lookup.

Safeguards: one-time codes; only the newest code per account is valid; per-account
30s rate limit against code spam; a 1-minute purge bounds the code table; the
websiteUserId is trusted only because the socket is loopback-only. The tag reaches
memory on confirm but disk only on the next save — a hard crash between loses it,
and the player just re-runs [link.

Verified end to end with a smart stub that reads the emitted code and confirms
it: link.request -> link.confirm -> link.ok, a bad code -> link.error, and the
tag observed in accounts.xml after a save. Evidence in docs/PLAN.md §15.

The [link command body is exposed as RequestLink(Mobile) so it can be driven in
tests without a client. Adds tools/stub_sidecar_link.ps1 and
tools/scaffolding/BridgeLinkProbe.cs.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

overlay/Scripts/Custom/Bridge/BridgeConfig.cs

@@ -18,6 +18,8 @@ namespace Server.Custom.Bridge
         public static int DecaySweepSeconds { get; private set; }
         public static int EconomySweepSeconds { get; private set; }
 
+        public static string LinkUrl { get; private set; }
+
         public static bool Enabled { get; private set; }
 
         public static void Configure()
@@ -38,6 +40,8 @@ namespace Server.Custom.Bridge
             DecaySweepSeconds = Config.Get("Bridge.DecaySweepSeconds", 60);
             EconomySweepSeconds = Config.Get("Bridge.EconomySweepSeconds", 300);
 
+            LinkUrl = Config.Get("Bridge.LinkUrl", "https://yoursite/link");
+
             if (QueueCap < 16)
                 QueueCap = 16;
         }