docs: ignore generated .ua trash directories

[chengweiv5]

Summary

• document .ua/.trash-*/ as local scratch data
• add the missing ignore rule to the main README and all seven translations
• keep the legacy .understand-anything/ substitution guidance intact

Root cause

The /understand cleanup flow moves temporary directories to .ua/.trash-<timestamp>/, but the “Share the Graph with Your Team” examples only ignored intermediate/ and diff-overlay.json. Following the documented example could therefore stage generated trash directories.

Impact

Users can copy the documented ignore block without accidentally committing .trash-* directories. Runtime behavior is unchanged.

Validation

• git diff --check
• verified all eight README variants contain the three expected ignore rules
• independently tested with git check-ignore that .ua/.trash-123/ is ignored while .ua/knowledge-graph.json remains trackable
• independently tested the equivalent legacy .understand-anything/ substitution