docs: move docs to RunicGateway/docs, repoint all references

Extracted docs/ (ADMIN_CONTROLS, INTEGRATION, PLAN, PROTOCOL_2, RESEARCH,
SHARD_PREREQS) into the central RunicGateway/docs repo under link/, with
full commit history preserved via git filter-repo.

The source cites these design docs by section throughout, so every in-repo
reference (C# + Rust comments, Bridge.cfg, and the READMEs) is repointed at
the new docs-repo URL. README references are rendered as markdown links; a
Documentation pointer section is added to the top-level README.

Docs repo: https://gitea.whitlocktech.com/RunicGateway/docs

overlay/Scripts/Custom/Bridge/BridgeAccounts.cs

@@ -8,7 +8,7 @@ using Server.Misc;
 namespace Server.Custom.Bridge
 {
     /// <summary>
-    ///     The account provisioning plane (docs/PROTOCOL_2.md Part A): website-driven account
+    ///     The account provisioning plane (https://gitea.whitlocktech.com/RunicGateway/docs/src/branch/main/link/PROTOCOL_2.md Part A): website-driven account
     ///     creation and unlinking. Companion to BridgeAccountLink (the in-game [link flow), which
     ///     is unchanged.
     ///
@@ -18,7 +18,7 @@ namespace Server.Custom.Bridge
     ///     Both handlers run on the Core thread (BridgeBoot marshals inbound lines through
     ///     Timer.DelayCall first), so they touch accounts freely.
     ///
-    ///     Trust model matches the admin plane (docs/ADMIN_CONTROLS.md §5): authorization lives on
+    ///     Trust model matches the admin plane (https://gitea.whitlocktech.com/RunicGateway/docs/src/branch/main/link/ADMIN_CONTROLS.md §5): authorization lives on
     ///     the website; the shard trusts the loopback + token socket and a required "actor" field.
     ///     The one shard-side floor on unlink is BridgeAdmin.Protected — a protected staff account is
     ///     never unlinkable from the web. The whole create plane is opt-in via SignupMode /