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/DashboardView.vue

@@ -259,7 +259,7 @@ function navServer() { router.push('/server') }
         <EmptyState
           icon="server"
           title="No server connected"
-          description="Install the companion agent on your host machine to begin managing your server from Corrosion."
+          description="Install the Corrosion host agent on your host machine to begin managing your server from Corrosion."
         >
           <template #action>
             <Button icon="server" @click="navServer">Set up server</Button>
@@ -404,7 +404,7 @@ function navServer() { router.push('/server') }
         <div class="dash__col dash__col--side">
 
           <!-- Resources — real stats from agent; null = '—' -->
-          <Panel title="Resources" subtitle="Companion agent telemetry">
+          <Panel title="Resources" subtitle="Host agent telemetry">
             <div class="solo-meters">
               <ResourceMeter
                 label="CPU"
@@ -418,7 +418,7 @@ function navServer() { router.push('/server') }
               />
             </div>
             <div v-if="soloCpu === null && soloRamMb === null" class="meters-note">
-              Resource metrics arrive via the companion agent heartbeat.
+              Resource metrics arrive via the host agent heartbeat.
               <Button size="sm" variant="ghost" icon="server" class="meters-cta" @click="navServer">
                 Agent setup
               </Button>