- Fix: Handle None content in messages to prevent Jinja2 'dict object has no attribute content' error
  - Added safety check in chat_completions function
  - Fixed _manual_format_messages to explicitly check for None
  - Fixed format_messages in VulkanBackend to ensure content is never None

- Fix: Always filter tool call format from output
  - Changed filter to run unconditionally (not just when tools are present)
  - Added extra regex patterns for JSON format tool calls like <tool>{...}</tool>

- Also fixed: Minor typos in comments (cket ->cket)