docs(installer): lead with the installer now that it is released

v0.1.0 shipped on 2026-08-07, so every doc that said "not released yet"
was wrong the moment the cutover merged.

- INSTALL.md: replace the pre-release status banner. The installer is the
  path the guide leads with; Appendix A is reframed as supported-not-
  deprecated, for hosts that cannot run the binary, operators who want to
  place files themselves, and development from a working tree.
- PLAN.md: status is Shipped, both cutover gates recorded as met (incl.
  the Windows 1053 handshake bug the real SCM run found), Phase 5 table
  and 5.4 closed out.
- README.md: point anyone setting up a shard at INSTALL.md first.
- link/link-README.md: mark the pre-split snapshot as historical, so its
  deploy.ps1 instructions stop reading as the setup path.

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

link/link-README.md

@@ -1,5 +1,12 @@
 # uo-link
 
+> **Historical snapshot**, from before the bridge was split into
+> [`RunicGateway/link`](https://gitea.whitlocktech.com/RunicGateway/link) (sidecar) and
+> [`RunicGateway/servuo-plugins`](https://gitea.whitlocktech.com/RunicGateway/servuo-plugins)
+> (plugin). Kept for the architecture notes below. **To set a shard up, use
+> [installer/INSTALL.md](../installer/INSTALL.md)** — `deploy.ps1` as described here is a developer
+> tool, not the operator path.
+
 ServUO ⇄ Rust sidecar bridge. The shard emits newline-delimited JSON over a loopback TCP socket; the sidecar owns the WebSocket the website consumes.
 
 ```