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/vite.config.ts

@@ -2,12 +2,18 @@ import { defineConfig } from 'vite'
 import vue from '@vitejs/plugin-vue'
 import tailwindcss from '@tailwindcss/vite'
 import { fileURLToPath, URL } from 'node:url'
+import { readFileSync } from 'node:fs'
+
+const pkg = JSON.parse(readFileSync(new URL('./package.json', import.meta.url), 'utf-8'))
 
 export default defineConfig({
   plugins: [
     vue(),
     tailwindcss(),
   ],
+  define: {
+    __APP_VERSION__: JSON.stringify(pkg.version),
+  },
   resolve: {
     alias: {
       '@': fileURLToPath(new URL('./src', import.meta.url)),