Five interrelated fixes from parallel Hephaestus sessions:
1. fix(repl): display assistant text after spinner (#2981, #2982, #2937)
- Added final_assistant_text() call after run_turn spinner completes
- REPL now shows response text like run_prompt_json does
2. fix(compact): handle Thinking content blocks (#2985)
- Added ContentBlock::Thinking variant throughout compact summarizer
- Prevents panic when /compact encounters thinking blocks
3. fix(prompt): provider-aware model identity (#2822)
- New ModelFamilyIdentity enum (Claude vs Generic)
- Non-Anthropic models no longer say 'I am Claude'
- model_family_identity_for() detects provider and sets identity
4. fix(openai): preserve DeepSeek reasoning_content (#2821)
- Stream parser now captures reasoning_content from OpenAI-compat
- Emits ThinkingDelta/SignatureDelta events for reasoning models
- Thinking blocks included in conversation history for re-send
5. feat(runtime): Thinking block support across codebase
- AssistantEvent::Thinking variant in conversation.rs
- ContentBlock::Thinking in session serialization
- Thinking-aware compact summarization
- Tests for thinking block ordering and content
Closes#2981, #2982, #2937, #2985, #2822, #2821
