fix(cli): resolve GritQL pattern not found error in pyenv environments

[starchou6]

Description:
This PR fixes the issue where langchain-cli migrate command fails when run in pyenv virtual environments. The problem occurs because the .grit directory is placed under a git-managed pyenv virtualenv, and GritQL honors parent .gitignore files, causing the .grit directory to be ignored and pattern definitions to be inaccessible.

The fix moves the .grit directory to a user cache location (~/.cache/langchain-cli/.grit) to avoid Git management conflicts. The implementation includes:

• Automatic creation of cache directory on first run
• Copying of .grit files from package to cache location
• Fallback mechanism to original behavior if source doesn't exist

Issue: Fixes #32779

Dependencies: None - uses only standard library modules (shutil, pathlib)

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1 Skipped Deployment

Project	Deployment	Preview	Comments	Updated (UTC)
langchain	Ignored	Preview		Sep 4, 2025 11:03pm

[codspeed-hq]

CodSpeed WallTime Performance Report

Merging #32815 will not alter performance

_{Comparing starchou6:fix/migrate-grit-dir-gitignore-conflict (2522232) with master (aa63de9)}

⚠️ Unknown Walltime execution environment detected

Using the Walltime instrument on standard Hosted Runners will lead to inconsistent data.

For the most accurate results, we recommend using CodSpeed Macro Runners: bare-metal machines fine-tuned for performance measurement consistency.

Summary

✅ 13 untouched benchmarks

[codspeed-hq]

CodSpeed Instrumentation Performance Report

Merging #32815 will not alter performance

_{Comparing starchou6:fix/migrate-grit-dir-gitignore-conflict (2522232) with master (aa63de9)}

Summary

✅ 14 untouched benchmarks