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

sidecar/src/web.rs

@@ -77,7 +77,7 @@ pub async fn serve(addr: &str, state: AppState) -> anyhow::Result<()> {
         .route("/economy", get(economy))
         .route("/champs", get(champs))
         // World-state boards (Protocol 2.0), served from the store so they answer without the shard
-        // and survive an outage with the last-known snapshot (docs/PROTOCOL_2.md §12.2).
+        // and survive an outage with the last-known snapshot (https://gitea.whitlocktech.com/RunicGateway/docs/src/branch/main/link/PROTOCOL_2.md §12.2).
         .route("/guilds", get(guilds))
         .route("/governors", get(governors))
         .route("/online", get(online))