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/builder.py

@@ -2,7 +2,7 @@
 
 import shutil
 from pathlib import Path
-from typing import Dict, Any, Optional
+from typing import Dict, Any, Optional, Union
 from jinja2 import Environment, FileSystemLoader, Template
 
 from gallery.config import GalleryConfig
@@ -22,7 +22,7 @@ from gallery.utils.processing import (
 )
 
 
-def get_template(template_dir: Optional[Path | str] = None):
+def get_template(template_dir: Optional[Union[Path, str]] = None):
     """
     Get the Jinja2 template for gallery rendering.
 
@@ -167,11 +167,16 @@ def copy_assets(
         gallery_root = Path(config.web_folder) / config.plot_root
         assets_dst = gallery_root.parent / "assets"
 
-        main_css_src = assets_src / "css" / "main.css"
-        main_css_dst = assets_dst / "css" / "main.css"
+        # Use the newest mtime across all source asset files as the staleness check,
+        # so any change to any JS/CSS file triggers a redeploy.
+        sentinel_dst = assets_dst / "css" / "main.css"
+        newest_src_mtime = max(
+            (f.stat().st_mtime for f in assets_src.rglob('*') if f.is_file()),
+            default=0,
+        )
+        dst_mtime = sentinel_dst.stat().st_mtime if sentinel_dst.exists() else 0
 
-        if (not assets_dst.exists() or
-                needs_update(main_css_src, main_css_dst)):
+        if not assets_dst.exists() or newest_src_mtime > (dst_mtime + 30):
             if assets_dst.exists():
                 shutil.rmtree(assets_dst)
             shutil.copytree(assets_src, assets_dst)