fix post-login blank page + rebrand login hero

- nginx: use alias for BASE_PATH fallback so static assets resolve
  correctly when deployed under a sub-path (fixes white page on K8s)
- base.html: remove dead template refs (chat, notes, projects) that
  caused html/template to fail silently with Content-Length: 0
- login hero: rebrand from "Chat Switchboard" to "Switchboard Core",
  update tagline and feature pills to reflect platform pivot

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

server/pages/templates/base.html

@@ -26,9 +26,7 @@
     <link rel="stylesheet" href="{{.BasePath}}/css/extension-surface.css?v={{.Version}}">
     <link rel="stylesheet" href="{{.BasePath}}/css/sw-shell.css?v={{.Version}}">
     <link rel="stylesheet" href="{{.BasePath}}/css/sw-debug.css?v={{.Version}}">
-    {{if eq .Surface "chat"}}{{template "css-chat" .}}{{end}}
-    {{if eq .Surface "notes"}}{{template "css-notes" .}}{{end}}
-    {{if eq .Surface "projects"}}{{template "css-projects" .}}{{end}}
+    {{/* gutted: css-chat, css-notes, css-projects templates removed */}}
     {{/* v0.27.0: Extension surface CSS — loaded from /surfaces/{id}/css/main.css */}}
     {{if and .Manifest (eq .Manifest.Source "extension")}}
     <link rel="stylesheet" href="{{.BasePath}}/surfaces/{{.Surface}}/css/main.css?v={{.Version}}">
@@ -93,12 +91,9 @@
 
     <div class="surface" id="surface">
         <div class="surface-inner" id="surfaceInner">
-        {{if eq .Surface "chat"}}{{template "surface-chat" .}}
-        {{else if eq .Surface "admin"}}{{template "surface-admin" .}}
+        {{if eq .Surface "admin"}}{{template "surface-admin" .}}
         {{else if eq .Surface "team-admin"}}{{template "surface-team-admin" .}}
-        {{else if eq .Surface "notes"}}{{template "surface-notes" .}}
         {{else if eq .Surface "settings"}}{{template "surface-settings" .}}
-        {{else if eq .Surface "projects"}}{{template "surface-projects" .}}
         {{else if and .Manifest (eq .Manifest.Source "extension")}}{{template "surface-extension" .}}
         {{else}}<div style="padding:20px">Unknown surface: {{.Surface}}</div>
         {{end}}
@@ -130,12 +125,9 @@
          workflow-surfaces.js removed. All surfaces use Preact SDK boot().
          Survivors: debug.js, repl.js (standalone, no old-layer deps). */}}
 
-    {{if eq .Surface "chat"}}{{template "scripts-chat" .}}{{end}}
     {{if eq .Surface "admin"}}{{template "scripts-admin" .}}{{end}}
     {{if eq .Surface "team-admin"}}{{template "scripts-team-admin" .}}{{end}}
-    {{if eq .Surface "notes"}}{{template "scripts-notes" .}}{{end}}
     {{if eq .Surface "settings"}}{{template "scripts-settings" .}}{{end}}
-    {{if eq .Surface "projects"}}{{template "scripts-projects" .}}{{end}}
     {{/* v0.27.0: Extension surface JS — loaded from /surfaces/{id}/js/main.js */}}
     {{if and .Manifest (eq .Manifest.Source "extension")}}
     <script type="module" nonce="{{.CSPNonce}}" src="{{.BasePath}}/surfaces/{{.Surface}}/js/main.js?v={{.Version}}"></script>