fix: REPL display, /compact panic, identity leak, DeepSeek reasoning, thinking blocks

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

rust/crates/runtime/src/lib.rs

@@ -131,8 +131,8 @@ pub use policy_engine::{
     PolicyEngine, PolicyRule, ReconcileReason, ReviewStatus,
 };
 pub use prompt::{
-    load_system_prompt, prepend_bullets, ContextFile, ProjectContext, PromptBuildError,
-    SystemPromptBuilder, FRONTIER_MODEL_NAME, SYSTEM_PROMPT_DYNAMIC_BOUNDARY,
+    load_system_prompt, prepend_bullets, ContextFile, ModelFamilyIdentity, ProjectContext,
+    PromptBuildError, SystemPromptBuilder, FRONTIER_MODEL_NAME, SYSTEM_PROMPT_DYNAMIC_BOUNDARY,
 };
 pub use recovery_recipes::{
     attempt_recovery, recipe_for, EscalationPolicy, FailureScenario, RecoveryContext,