Add Lark digital clone scan command

[maxliux5]

Summary

• Add loopx lark-digital-clone scan for generating local reviewed Lark reply drafts, weekly material, and candidate LoopX todos.
• Keep external writes disabled: generated send commands remain dry-run previews and require user approval before any real send path.
• Add fixture mode so the command can be validated with synthetic public messages without reading Lark.

Boundary

• Does not include local .local/ artifacts, real Lark message payloads, the prototype HTML viewer, LaunchAgent config, or send backend.
• Default artifacts are written under .local/lark-digital-clone/latest.
• Real Lark reads require --execute-read; without it, Lark calls stay as dry-run previews.

Validation

• python3 -m py_compile loopx/capabilities/lark_digital_clone/__init__.py loopx/capabilities/lark_digital_clone/scan.py loopx/capabilities/lark_digital_clone/cli.py loopx/cli.py examples/lark-digital-clone-scan-smoke.py
• python3 examples/lark-digital-clone-scan-smoke.py
• python3 -m loopx.cli --format json lark-digital-clone scan --at-me --since 24h --fixture-json <synthetic fixture> --out-dir <tmp>/out --skip-auth-check
• Public/private scan over changed files: only benign API field names such as page_token matched.