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

patches/BridgeModerationAudit.cs

@@ -9,7 +9,7 @@ namespace Server.Custom.Bridge
     /// <summary>
     ///     Forwards IN-GAME uses of the write-plane verbs to the website as admin.audit
     ///     (origin=in-game), so the site's moderation log is complete regardless of whether an action
-    ///     came from the website or a staff member in the game client. See docs/ADMIN_CONTROLS.md §5.5.
+    ///     came from the website or a staff member in the game client. See https://gitea.whitlocktech.com/RunicGateway/docs/src/branch/main/link/ADMIN_CONTROLS.md §5.5.
     ///
     ///     Two sources, mirroring how the shard records each:
     ///       - ban / kick: resolved with their target inside the stock generic command, which logs a