Add repo validation workflow, conflict-fixer script, and UI/config improvements

[VHugoDevIA]

Motivation

• Add automated repository validation to catch merge artifacts and Python compile errors early via CI.
• Provide a small tool to quickly remove common merge/branch artefacts that cause IndentationError and similar issues.
• Improve configuration handling and UI robustness to avoid conflicts and make results sorting/interaction more reliable.

Description

• Add GitHub Actions workflow /.github/workflows/validate.yml that runs python scripts/validate_repo.py on pull requests and pushes to main.
• Add scripts/validate_repo.py which scans main.py and src/*.py for conflict markers and branch artefacts and runs compileall on main.py and src.
• Add scripts/fix_conflict_artifacts.py which can sanitize files by removing conflict tokens and common branch artefacts and creates a .bak backup when run with --write.
• Modify src/app.py to migrate config to a per-user folder (~/.duplicate-file-cleaner/config.json), add robust JSON read/write helpers, and fallback to legacy config.json; also improve UI layout (splitters), add a toggleable filters panel, numeric sorting via SortableTreeWidgetItem, group expand/collapse actions, and selection-load guard (_selection_loaded).
• Update README.md with a quick resolution section describing how to use the conflict-fixer script, update .gitignore to include config.json, and replace the root config.json content with {}; remove several stray placeholder files.

Testing

• Ran python scripts/validate_repo.py locally which checks for conflict markers and attempts to compile main.py and src, and it completed successfully.
• Added CI workflow validate.yml to run the same validation on PRs and pushes to main, ensuring automated checks will run for future changes.

---

Codex Task

[chatgpt-codex-connector]

💡 Codex Review

Duplicate-File-Cleaner/scripts/validate_repo.py

Line 13 in 66dd58b

targets = [ROOT / "main.py", *(ROOT / "src").rglob("*.py")]

Include scripts in repository validation

The validation script currently limits conflict-marker scanning to main.py and src/**/*.py, so CI can still pass when a Python file under scripts/ is broken or contains merge artifacts. In this commit that means scripts/fix_conflict_artifacts.py is not validated at all, which undermines the new “repo validation” workflow and allows regressions in maintenance tooling to ship undetected; expand the target set (and compile step) to cover scripts/**/*.py as well.

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".