Refactor: Remove obsolete JavaScript managers and utilities

- Deleted NavigationManager, RecentPlotsManager, SearchManager, SortManager, StatsManager, ThemeManager, Utils, and ViewManager classes.
- Updated gallery builder to improve asset copying logic with a more efficient modification time check.
- Cleaned up gallery HTML template by removing subdirectory listing and embedding gallery data as JSON.
- Added CLAUDE.md for project documentation and guidelines.

gallery/api.py

@@ -260,8 +260,11 @@ def generate(
                 print(f"Warning: Could not render gallery root: {e}")
             # Don't fail, gallery is still usable
 
-        if verbose:
-            print(f"✓ Gallery generated successfully at {gallery_root}")
+        plot_count = _count_gallery_plots(gallery_root)
+        if plot_count == 0:
+            print(f"Warning: Gallery at {gallery_root} appears to be empty — no plot files found!")
+        else:
+            print(f"✓ Gallery generated at {gallery_root} — {plot_count} plots total")
 
         return True
 
@@ -271,6 +274,15 @@ def generate(
         return False
 
 
+def _count_gallery_plots(gallery_root: Path) -> int:
+    """Recursively count plot files (PDFs and HTMLs, excluding index.html) in the gallery output."""
+    count = 0
+    for f in gallery_root.rglob('*'):
+        if f.is_file() and f.suffix.lower() in ('.pdf', '.html') and f.name != 'index.html':
+            count += 1
+    return count
+
+
 def _is_writable(path: Path) -> bool:
     """
     Check if a path is writable.