Add dry-run and check modes to dev-tools sync

[coisa]

Objective

Add --dry-run and --check modes to dev-tools:sync so maintainers can inspect pending synchronization changes before writing files, and optionally confirm replacements interactively in terminal sessions.

Current Limitation

dev-tools:sync performs file and repository mutations directly. Maintainers of consumer repositories need a safe way to preview changes, identify stale managed files, and use a CI-friendly mode that fails when sync-managed files are drifted.

Proposed Work

Add three execution modes:

• --dry-run: report the changes sync would make without writing files or running mutating Git operations.
• --check: report whether the repository is in sync and return a non-zero exit code when changes would be required.
• --interactive: when running in an interactive terminal, show detected drift and ask whether each managed file should be replaced.

The default dev-tools:sync behavior should remain non-interactive. Prompting should only happen when --interactive is explicitly requested and the input is interactive.

Scope

• Cover all existing sync phases where practical: Composer metadata, workflow stubs, .editorconfig, Dependabot, wiki setup, .gitignore, .gitattributes, skills, license, and Git hooks.
• Ensure --dry-run does not write files, create symlinks, initialize hooks, or add submodules.
• Ensure --check is suitable for CI and exits non-zero on detected drift or missing managed assets.
• Reuse or prepare drift/status logic from sync phases rather than shelling out blindly.
• Surface drift details in output, including affected phase, path, and text diffs where available.
• Keep --interactive optional and TTY-aware so Composer hooks and CI runs do not block on prompts.

Non-goals

• Implementing selective --only or --skip sync phases.
• Changing default sync behavior.
• Forcing prompts during Composer hooks, CI, or non-interactive sessions.
• Guaranteeing dry-run support for unsupported external tools in the first pass; unsupported phases should report that clearly.

Acceptance Criteria

Delivery Criteria

• dev-tools:sync --dry-run reports planned changes without modifying the working tree.
• dev-tools:sync --check exits 0 when no sync changes are needed.
• dev-tools:sync --check exits non-zero when managed files are missing or drifted.
• dev-tools:sync --interactive prompts before replacing drifted managed files when input is interactive.
• Dry-run/check output identifies the affected sync phase and path.
• Drift output includes text diffs when available and clear fallbacks for non-diffable files.
• Tests cover dry-run no-write behavior, check-mode exit codes, and interactive replace decisions.

Architectural / Isolation Criteria

• Sync phases expose inspectable planned actions before mutation.
• SyncCommand remains orchestration-focused.
• The implementation keeps output deterministic for CI logs and tests outside explicit interactive mode.