fix: live-reload theme CSS vars on editor save and frontmatter changes

Wire notifyThemeSaved through the frontmatter update chain so CSS
variables update immediately when:
- The user edits a theme note in raw mode and presses Cmd+S
- A frontmatter property is changed via the inspector panel

Also expose CodeMirror EditorView on the DOM for Playwright test access,
add unit tests for onNotePersisted, and a new Playwright smoke test
that verifies the full raw-editor → save → CSS-vars-update flow.

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

src/hooks/useCodeMirror.ts

@@ -126,6 +126,9 @@ export function useCodeMirror(
 
     const view = new EditorView({ state, parent })
     viewRef.current = view
+    // Expose EditorView on the parent DOM for Playwright test access
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    ;(parent as any).__cmView = view
 
     // When CSS zoom changes on the document, CodeMirror's cached measurements
     // (scaleX/scaleY, line heights, character widths) become stale because
@@ -136,6 +139,8 @@ export function useCodeMirror(
 
     return () => {
       window.removeEventListener('laputa-zoom-change', handleZoomChange)
+      // eslint-disable-next-line @typescript-eslint/no-explicit-any
+      delete (parent as any).__cmView
       view.destroy()
       viewRef.current = null
     }