feat(cli): add search context lines

[vinnytherobot]

Summary

• Add grep-style search context for stream output via --context/-C, --before-context/-B, and --after-context/-A.
• Keep context scoped to --search queries and reject ambiguous context usage without a search term.
• Bump package version to 0.5.0 and document the release in CHANGELOG.md.
• Add CLI coverage for context output and validation behavior.
• Update README/API docs with context usage examples.
• Fix .gitignore to ignore the actual AGENTS.md file.

Technical Details

The stream renderer now separates non-search filters from search matching. Level, min-level, and time filters are applied first, then iter_search_context() selects matching entries plus before/after neighbors without duplicating overlapping context windows.

--context acts as a symmetric shorthand, while --before-context and --after-context can override each side independently. Context is intentionally limited to standard stream output and is rejected with dashboard mode.

Validation

• pytest -q
• ruff check .
• pytest --cov=logscope --cov-report=term-missing
• python -m build

[github-actions]

PR Check Summary

• Conventional title: feat(cli): add search context lines
• Tests updated when code changes: true
• Docs updated when code changes: true