bug: flet clean deletes unrelated build directories without validating the project

Duplicate Check

• I searched existing issues for flet clean and found no duplicate report of this behavior.

Describe the bug

flet clean <path> accepts any existing directory and recursively deletes its build/ child without checking whether the directory is a Flet project or whether the build output was generated by Flet. There is no confirmation or explicit override required for unrecognized directories.

A mistyped path in a script or automation can therefore delete an unrelated project's build output. Running flet clean from the wrong working directory has the same risk because the path defaults to ..

Code sample

This reproduction confines all files to a newly created temporary directory:

import subprocess
import tempfile
from pathlib import Path

with tempfile.TemporaryDirectory(prefix="flet-clean-repro-") as tmp:
    unrelated_project = Path(tmp) / "unrelated-project"
    build_dir = unrelated_project / "build"
    build_dir.mkdir(parents=True)
    artifact = build_dir / "unrelated-artifact.txt"
    artifact.write_text("This output was not generated by Flet.\n")

    subprocess.run(["flet", "clean", str(unrelated_project)], check=True)
    print(f"Unrelated artifact still exists: {artifact.exists()}")

To reproduce

1. Use a Flet CLI version containing the current clean command.
2. Run the sample above. The target has no Flet application, project configuration, or Flet-generated artifacts.
3. The handler deletes the entire build/ directory; the sample should print Unrelated artifact still exists: False.

This report is based on source inspection and the existing test cases; the sample above has not been executed as part of filing this report.

Expected behavior

Cleaning an unrecognized directory should preserve its build output unless the caller explicitly opts into deleting it. A mistaken path should not silently remove an unrelated project's files.

Flet version

Source checkout at commit 59f759c4687c7188c1a813bcda139794ef3ae310. Released-version scope has not been verified.

Operating System

Inspected on macOS. The affected code has no platform-specific guard.

Regression

Unknown.

Suggestions

Consider checking a Flet-generated build marker or another reliable project identifier before deletion, with an explicit --force override for unrecognized directories. Account for Flet apps that do not have project metadata, and ensure non-interactive automation does not silently bypass the guard.

Additional details

• Path handling and deletion: the only target validation is app_path.is_dir(), followed by a check that build exists and shutil.rmtree(build_dir).
• Existing test: test_clean_respects_path_argument expects deletion in a directory with no Flet project files.
• The command was requested in #6233.