feat: add shared Toolbox header and themes

README.md

@@ -6,7 +6,7 @@ file dialogs where available. XSLT is executable code, however: a trusted
 stylesheet may access browser or network resources, so processing is not
 described as guaranteed local-only.
 
-The application is independently deployable and also implements Toolbox Contract v1. When launched with a same-origin `?toolbox=<catalog URL>` context, the shared application shell adds toolbox navigation and an application switcher; without that context, the same build runs standalone.
+The application is independently deployable and also implements Toolbox Contract v1. The shared top bar keeps the app title centered and provides Help, its Gitea source link, persistent System/Light/Dark personalization, and app selection. When launched with a same-origin `?toolbox=<catalog URL>` context, the Apps menu includes the catalogue tools; without that context, the same build runs standalone.
 
 ## Features in this MVP
 
@@ -17,6 +17,7 @@ The application is independently deployable and also implements Toolbox Contract
 - CodeMirror editors with:
   - line numbers
   - XML syntax highlighting
+  - theme-aware light and dark editor, gutter, and highlighting palettes
   - editor undo/redo
   - cut/copy/paste helpers
   - find support via CodeMirror shortcuts
@@ -36,7 +37,7 @@ The application is independently deployable and also implements Toolbox Contract
 - Confirmation dialog before destructive overwrites
 - LocalStorage persistence
 - Approximate “explain transformation” table after a run
-- Shared toolbox shell with standalone fallback, application switching, and the XSLT-specific Help action
+- Shared toolbox shell with standalone fallback, unified Help/source controls, personalization, and application switching
 - Relocatable static output for deployment at root or nested paths
 
 ## SaxonJS note
@@ -101,6 +102,10 @@ Toolbox mode is contextual rather than a separate build:
 
 An unavailable or invalid catalogue falls back to standalone operation.
 
+## Appearance
+
+Use **Personalize** in the shared top bar to select System, Light, or Dark. The choice is stored only in this browser using the same preference record as the Toolbox Portal, so it follows you between current Toolbox apps on the same origin. System mode follows the operating-system color preference. CodeMirror is reconfigured when the effective palette changes, including its editor background, gutters, active line, and XML syntax colors.
+
 ## Release archive
 
 After a successful build, create the deterministic application ZIP and SHA-256 sidecar with: