fix: unify theme system - fix theme switching persistence

- Unified localStorage key to 'theme-preference' across all components
- Fixed header.tsx using wrong localStorage key ('theme' instead of 'theme-preference')
- Added localStorage hybrid persistence for instant theme changes
- Removed router.refresh() which was causing stale data revert
- Replaced Blue theme with Sepia
- Consolidated auth() calls to prevent race conditions
- Updated UserSettingsData types to include all themes

.claude/commands/bmad/core/tasks/shard-doc.md

@@ -0,0 +1,9 @@
+---
+description: 'Splits large markdown documents into smaller, organized files based on level 2 (default) sections'
+---
+
+# Shard Document
+
+LOAD and execute the task at: _bmad/core/tasks/shard-doc.xml
+
+Follow all instructions in the task file exactly as written.