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>

CHANGELOG.md

@@ -2,6 +2,32 @@
 
 All notable changes to Switchboard Core are documented here.
 
+## [Unreleased] — v0.2.7
+
+### Changed
+
+- **localStorage namespace**: Renamed `cs-appearance` key to `sb-appearance`
+  across appearance settings, base template, and workflow template. One-time
+  migration preserves existing user preferences.
+- **Policy-gating tests**: Replaced stale `allow_user_byok` / `allow_user_personas`
+  assertions with `allow_registration` check (the only policy still in admin UI).
+
+### Removed
+
+- **Dead BYOK nav section** in user settings: empty `BYOK_ITEMS` array,
+  `byokEnabled` state, "BYOK Enabled" footer badge, and the nav group
+  that rendered an empty section.
+- **Dead personas gate**: `personasEnabled` state and `.filter()` on
+  NAV_ITEMS for a `gate` property no items have. `auth.permissions.changed`
+  listener removed (existed solely for BYOK + personas state).
+- **Dead Message Font Size**: Slider, `msgFont` state, and `--msg-font`
+  CSS variable application from appearance section and base template.
+- **Dead policy defaults**: `allow_user_byok` and `allow_user_personas`
+  removed from `PolicyDefaults`, profile bootstrap, permissions handler,
+  and `PublicSettings`. Test seed data cleaned.
+
+---
+
 ## [Unreleased] — v0.2.6
 
 ### Changed