fix(panel): real auto-updating version + remove fake agent footer; rename companion -> Corrosion host agent

Version badge: was hardcoded '1.0.8' — now single-sourced from frontend/package.json (1.0.0) via Vite define __APP_VERSION__, so it auto-updates on release. Sidebar agent footer: removed the FABRICATED 'asgard-01' host name and the fake 'Agent v1.0.8' line — now shows real server.connection data, or an honest 'No host agent connected' empty state when nothing is deployed (the operator's actual state). Renamed 'Companion agent' -> 'Corrosion host agent' across the UI (ServerView/SetupWizard/Dashboard/Plugins), the binary names (corrosion-host-agent-<os>-<arch>) + CDN path (/host-agent/), the Go Makefile build output, and the Gitea CI workflow — frontend download links and CI output now match. Marketing hero mock host names neutralized (asgard-01 -> rust-host/dune-host/conan-host). DB column names (companion_last_seen) left intact. Build green; zero 'asgard'/'1.0.8' remain in frontend/src.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/views/admin/PluginsView.vue

@@ -485,7 +485,7 @@ onMounted(() => {
       </Panel>
 
       <Alert tone="info">
-        The plugin will be registered in your plugin list immediately. Your companion agent must be connected
+        The plugin will be registered in your plugin list immediately. Your host agent must be connected
         for the file to be delivered to the game server. If the agent is offline, re-upload once it reconnects.
       </Alert>
     </div>