v0.6.0

Changelog

• cf3259e docs(i18n): add internationalization documentation to README
• 8b223f2 feat(i18n): add 'tu lang' command for language switching
• 7e1e653 feat(i18n): add Language config field and --lang global flag
• ed2e05e feat(i18n): add i18n package with en/zh dictionaries and T() lookup
• cc45c01 feat(i18n): translate all command Short/Long, flags, and cobra framework labels
• 9fb6533 feat(i18n): translate all runtime output, TUI, and error messages (Layers 2-3)
• b1a54af fix: bare quota filter selects the provider when it names one
• 1bee7e8 fix: make the system keyring probe fully disableable via env var
• 300ade4 fix: resolve QA review findings across config, providers, auth, cmd, i18n