Remove pre-package-restructure cruft and dead features

Delete the top-level implementation superseded by the gallery/ package
conversion (generate_gallery.py, orchestration/, root templates/ and
assets/, python/ scripts), stray scratch files, and docs describing a
container/GitLab-CI coverage workflow that no longer exists. Also drop
two half-wired, never-invoked features: the backup_folder config/TUI
option (create_backup() was never called from the pipeline) and the
unfinished export-to-LaTeX JS/CSS. Update README's install instructions
to the current Gitea remote.

gallery/utils/backup.py

@@ -1,37 +0,0 @@
-"""Backup utilities for gallery."""
-
-import datetime
-import zipfile
-from pathlib import Path
-
-
-def create_backup(web_folder: Path, backup_folder: Path) -> bool:
-    """
-    Create a backup of the web folder.
-
-    Args:
-        web_folder: Path to the web folder to backup
-        backup_folder: Path to the backup directory
-
-    Returns:
-        True if backup was created successfully, False otherwise
-    """
-    try:
-        today = datetime.date.today().strftime("%Y%m%d")
-        backup_name = f"backup-{today}.zip"
-        backup_path = backup_folder / backup_name
-
-        backup_folder.mkdir(parents=True, exist_ok=True)
-
-        if backup_path.exists():
-            return True
-
-        with zipfile.ZipFile(backup_path, "w", zipfile.ZIP_DEFLATED) as zipf:
-            for path in web_folder.rglob("*"):
-                if path.is_file():
-                    arcname = path.relative_to(web_folder.parent)
-                    zipf.write(path, arcname)
-        return True
-    except Exception as e:
-        print(f"Warning: Could not create backup: {e}")
-        return False