Fix stale plugin docs and dead links

- unraid_api.php comment still told you to run Deployment/deploy.sh,
  deleted a while back
- VaraverkSettings.page linked to a CHANGELOG.md that doesn't exist
  anywhere in the repo
- Manual-Plugin.md / README-Plugin.md described manually heredoc-ing the
  .plg locally and a .txz-based install that isn't wired up — rewritten
  to describe the actual install flow (raw .plg URL via Plugins ->
  Install Plugin), with plugin_setup.sh's dev-symlink role called out
  separately from that install path

Plugin/unraid/include/unraid_api.php

@@ -247,7 +247,7 @@ function vv_local_host_stats(): array {
 
 // ── Confirmed schema (Unraid 7.3, introspected 2026-05-31) ───────────────────
 // Adding a new host: add HOSTn="hostname" to master.conf and HOSTn_UNRAID_API_KEY
-// to hostn.conf, then run Deployment/deploy.sh. No schema work needed.
+// to hostn.conf, then push and pull as usual. No schema work needed.
 //
 // If a future Unraid version renames a field, the affected function falls back
 // to local reads and the api banner lists the fallback — fix by updating the GQL.