Add session management, readline history, context compression, --ctx, --micro flags, and context counter in prompt

Fix streaming display in coder CLI - use iter_lines for immediate output, remove threading timer, simplify tool parsing

- Add generate_chat() and generate_chat_stream() methods to VulkanBackend
- These use create_chat_completion() which properly applies model's chat template
- Fallback to manual formatting if create_chat_completion fails
- Update API endpoints to pass messages dict directly instead of formatted prompt
- Fixes garbled output with Qwen3 and other models that use custom chat templates

- Use apply_chat_template() to properly format messages for each model
- This ensures Qwen3 and other models get their correct chat format
- Fallback to <|im_start|>/|im_end|> format if apply_chat_template fails
- Fixes garbled output with <|system|> tags appearing in responses

- Add --tiny command line flag for models under 3B parameters
- Add 'tiny' field to config file (can be set via config or CLI)
- Add TINY_MODEL_SYSTEM_PROMPT with simplified instructions
- Emphasizes spacing rules for models that produce garbled output
- Shorter, more direct system prompt for limited context windows