Fix template rendering issue and improve export functionality

- Fix template rendering by storing rendered HTML in variable before writing
  This resolves subdirectories not appearing in navigation despite being
  correctly detected and included in template variables
- Add missing template variables (paths.work_dir) to gallery config
- Add CGI refresh handler for web-based gallery regeneration
- Improve PDF export functionality with better error handling
- Add ESC key shortcut documentation for exiting selection mode
- Enhanced export manager with proper dependency checking

Fixes issue where new subdirectories were detected but not displayed
in browser navigation due to incomplete template rendering.

generate_gallery.py

@@ -15,6 +15,8 @@ Features:
 
 import subprocess
 import shutil
+import os
+import sys
 from pathlib import Path
 from typing import Dict, Any, Optional
 from jinja2 import Environment, FileSystemLoader
@@ -114,6 +116,7 @@ def build_gallery(source_dir: Path, web_dir: Path,
     current_metadata = merge_metadata(inherited_metadata, folder_metadata)
 
     pdf_files = list(source_dir.glob("*.pdf"))
+
     subdirs = [d for d in source_dir.iterdir() if d.is_dir()]
 
     items = []
@@ -188,16 +191,18 @@ def build_gallery(source_dir: Path, web_dir: Path,
         assets_path = "../" * (depth + 1) + "assets"
 
     with output_html.open("w") as f:
-        f.write(template.render(
+        rendered_html = template.render(
             title=title,
             items=items,
             subdirs=subdir_names,
             relpath=str(relative_path),
+            paths=CONFIG.paths,
             ui=CONFIG.ui,
             stats=stats,
             folder_metadata=current_metadata,
             assets_path=assets_path
-        ))
+        )
+        f.write(rendered_html)
 
     print(f"Generated {output_html}")
 
@@ -262,6 +267,21 @@ def format_file_size(size_bytes: int) -> str:
     return f"{size:.1f} {size_names[i]}"
 
 
+def refresh_gallery_cgi():
+    """
+    CGI handler to refresh the gallery from a web request.
+    Outputs a minimal HTTP response and triggers gallery regeneration.
+    """
+    import traceback
+    print("Content-Type: text/plain\n")
+    try:
+        main()
+        print("Gallery refreshed successfully.")
+    except Exception as e:
+        print(f"Error refreshing gallery: {e}")
+        traceback.print_exc(file=sys.stdout)
+
+
 def main() -> None:
     """
     Main entry point for gallery generation.
@@ -356,6 +376,7 @@ def main() -> None:
                     items=items,
                     subdirs=[],
                     relpath=source.name,
+                    paths=CONFIG.paths,
                     ui=CONFIG.ui,
                     stats=stats,
                     folder_metadata={},
@@ -375,7 +396,12 @@ def main() -> None:
                   f"directory nor a PDF file")
 
     print("Done")
+    # No copying of this script to CGI location
 
 
 if __name__ == "__main__":
-    main()
+    # If run as CGI, call the CGI handler
+    if 'GATEWAY_INTERFACE' in os.environ:
+        refresh_gallery_cgi()
+    else:
+        main()