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/BridgeAccountLink.cs

@@ -18,7 +18,7 @@ namespace Server.Custom.Bridge
     ///          and replies link.ok. The tag persists to accounts.xml across restarts.
     ///
     ///     The code table and the account write both live on the Core thread. The websiteUserId in
-    ///     link.confirm is trusted only because the socket is loopback-only (docs/PLAN.md §2); if the
+    ///     link.confirm is trusted only because the socket is loopback-only (https://gitea.whitlocktech.com/RunicGateway/docs/src/branch/main/link/PLAN.md §2); if the
     ///     sidecar ever moves off-host, gate it behind a shared secret.
     /// </summary>
     public static class BridgeAccountLink