refactor: migrate to src/ package + add DinD-based E2E runner with debug artifacts

- Replace legacy standalone scripts with a proper src-layout Python package
  (baudolo backup/restore/configure entrypoints via pyproject.toml)
- Remove old scripts/files (backup-docker-to-local.py, recover-docker-from-local.sh,
  databases.csv.tpl, Todo.md)
- Add Dockerfile to build the project image for local/E2E usage
- Update Makefile: build image and run E2E via external runner script
- Add scripts/test-e2e.sh:
  - start DinD + dedicated network
  - recreate DinD data volume (and shared /tmp volume)
  - pre-pull helper images (alpine-rsync, alpine)
  - load local baudolo:local image into DinD
  - run unittest E2E suite inside DinD and abort on first failure
  - on failure: dump host+DinD diagnostics and archive shared /tmp into artifacts/
- Add artifacts/ debug outputs produced by failing E2E runs (logs, events, tmp archive)

https://chatgpt.com/share/694ec23f-0794-800f-9a59-8365bc80f435

src/baudolo/backup/shell.py

@@ -0,0 +1,26 @@
+from __future__ import annotations
+
+import subprocess
+
+
+class BackupException(Exception):
+    """Generic exception for backup errors."""
+
+
+def execute_shell_command(command: str) -> list[str]:
+    """Execute a shell command and return its output lines."""
+    print(command, flush=True)
+    process = subprocess.Popen(
+        [command],
+        stdout=subprocess.PIPE,
+        stderr=subprocess.PIPE,
+        shell=True,
+    )
+    out, err = process.communicate()
+    if process.returncode != 0:
+        raise BackupException(
+            f"Error in command: {command}\n"
+            f"Output: {out}\nError: {err}\n"
+            f"Exit code: {process.returncode}"
+        )
+    return [line.decode("utf-8") for line in out.splitlines()]