Release v0.6.3

Multi-Provider Translation Support

Features:
- Add Google Gemini API support (gemini-2.5-flash, gemini-2.5-pro)
- Add Anthropic Claude API support (claude-sonnet-4-5, claude-opus-4-5, claude-haiku-4-5)
- Migrate config from [deepl] to [translation] section with unified provider field
- Add intuitive rate limit format: 50m (RPM), 5s (RPS), or raw milliseconds
- Implement automatic retry logic with exponential backoff for rate limit errors (HTTP 429/503)
- Add configurable max_retries setting (default: 3)
- Support inline comments in config file (api_key = value # comment)
- Standardize logging with INF/WRN/ERR/SUC tags across all translators

Breaking Changes:
- Config section renamed from [deepl] to [translation]
- New provider field required (deepl, gemini-2.5-flash, claude-sonnet-4-5, etc.)
- Old [deepl] section still works with deprecation warning

Bug Fixes:
- Fix CI build warning for system() return value check