Feat v0.2.7 user settings audit (#11)

Audit all 6 user settings sections. Remove dead chat-era code,
rename localStorage namespace, clean up stale backend policies.

- Remove BYOK nav section (empty BYOK_ITEMS, byokEnabled state,
  "BYOK Enabled" badge) and personas gate filter from settings nav
- Remove auth.permissions.changed listener (existed solely for
  dead BYOK + personas state)
- Remove Message Font Size slider, msgFont state, and --msg-font
  CSS variable application from appearance section and base template
- Rename localStorage key cs-appearance → sb-appearance with
  one-time migration preserving existing user preferences
- Remove allow_user_byok and allow_user_personas from PolicyDefaults,
  profile bootstrap, permissions handler, PublicSettings, and test seeds
- Remove orphaned .settings-nav-footer CSS class
- Replace stale policy-gating test assertions with allow_registration

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

server/pages/templates/base.html

@@ -51,11 +51,11 @@
                 if (fav) fav.href = fav.href.replace(/favicon(-light)?\.svg/, resolved === 'light' ? 'favicon-light.svg' : 'favicon.svg');
             } catch(e) {}
         })();
-        // Early appearance — apply scale + msg font from localStorage on all surfaces.
+        // Early appearance — apply scale from localStorage on all surfaces.
         // Scale uses transform on .surface-inner so shell stays fixed, content fills viewport.
         (function() {
             try {
-                var p = JSON.parse(localStorage.getItem('cs-appearance') || '{}');
+                var p = JSON.parse(localStorage.getItem('sb-appearance') || '{}');
                 if (p.scale && p.scale !== 100) {
                     var s = p.scale / 100;
                     document.addEventListener('DOMContentLoaded', function() {
@@ -63,7 +63,6 @@
                         if (el) { el.style.transform = 'scale('+s+')'; el.style.transformOrigin = 'top left'; el.style.width = (100/s)+'%'; el.style.height = (100/s)+'%'; }
                     });
                 }
-                if (p.msgFont && p.msgFont !== 14) document.documentElement.style.setProperty('--msg-font', p.msgFont + 'px');
             } catch(e) {}
         })();
     </script>

server/pages/templates/workflow.html

@@ -163,7 +163,7 @@
     <script>
         (function() {
             try {
-                var p = JSON.parse(localStorage.getItem('cs-appearance') || '{}');
+                var p = JSON.parse(localStorage.getItem('sb-appearance') || '{}');
                 var mode = p.theme || 'system';
                 var resolved = mode;
                 if (mode === 'system') resolved = window.matchMedia('(prefers-color-scheme: dark)').matches ? 'dark' : 'light';