docs: fix misleading OAuth credential rename/move instructions

docs: add CHANGELOG.md and update README/CLAUDE.md for v0.2.0

refactor: remove dead code and fix minor issues across codebase

refactor(auth): extract shared _save_token_secure helper, fix dir permissions

refactor(drive): remove dead _normalize_drive_query function

fix(drive): add auth retry to drive_list_recursive mid-traversal

fix(main): handle KeyboardInterrupt and BrokenPipeError gracefully

fix(drive): reject files over 10 MB before downloading into memory

feat(gmail): add max_length parameter to gmail_get_message

fix(drive): add pagination to drive_list to return all files in folder

fix(sheets): use full sheet range instead of hardcoded A1:Z1000

fix(gmail): recurse into all multipart MIME types for body extraction

fix(test): correct JSON nesting assertion in test_config_json_outputs_json

perf(gmail): batch message fetches in gmail_search (N+1 -> 1 HTTP call)

fix(gmail,drive): handle non-UTF-8 content without crashing