Add KiloCode Claude provider comparison to review document

- Add KiloCode implementation analysis (vendors/kilocode/packages/opencode/src/provider/)
- Compare KiloCode's AI SDK approach (@ai-sdk/anthropic) vs direct HTTP
- Document KiloCode's features: automatic prompt caching, thinking support,
  message validation, reasoning variants, model management
- Add comparison tables for architecture, message conversion, streaming,
  headers, model resolution, reasoning/thinking support, prompt caching
- Document KiloCode exclusive features: empty content filtering, tool call ID
  sanitization, duplicate reasoning fix, provider option remapping,
  Gemini schema sanitization, unsupported part handling
- Update summary with KiloCode strengths and additional improvement areas