perf: reduce LLM input tokens by ~50% via prompt deduplication

- Remove JSON appendix from user_prompt (saves ~3000 chars, 85% reduction)
- Consolidate identity: remove English system_prompt identity, merge into agent_prompt Chinese identity
- Simplify system_prompt output rules: keep only Language Requirement, remove Answer Rules (duplicate with agent_prompt)
- Enhance follow-up context: include more divination_derived fields (changing_yaos, fushen, wu_xing, etc.)
- Fix bug: lowerName -> lower_name in user_prompt (Pydantic snake_case)
- Update tests to reflect new prompt structure

backend/tests/unit/test_agentscope_prompts.py

@@ -34,7 +34,7 @@ def test_system_prompt_enforces_ai_language_and_identity_signals() -> None:
         now_utc=datetime.now(timezone.utc),
     )
 
-    assert "ai_language=en-US" in prompt
+    assert '"ai_language":"en-US"' in prompt
     assert (
         "interface_language and country are weak signals for user identity inference"
         in prompt
@@ -65,8 +65,7 @@ def test_agent_prompt_keeps_only_identity_and_domain_flow() -> None:
 
     assert "[输出约束]" not in prompt
     assert "[安全与拒答]" not in prompt
-    assert "[六爻分析流程]" in prompt
-    assert "匹配 ai_language" in prompt
+    assert "[procedure]" in prompt
     assert "段间用\\n\\n" in prompt
     assert "优先四字表达，简洁且可复述" not in prompt
 
@@ -94,7 +93,7 @@ def test_system_prompt_sanitizes_invalid_language_and_country() -> None:
         now_utc=datetime.now(timezone.utc),
     )
 
-    assert "ai_language=zh-CN" in prompt
+    assert '"ai_language":"zh-CN"' in prompt
     assert '"interface_language":"zh-CN"' in prompt
     assert '"country":"CN"' in prompt
 
@@ -113,11 +112,9 @@ def test_system_prompt_sections_are_not_duplicated() -> None:
 
 
 def test_system_prompt_requires_paragraph_breaks_for_answer() -> None:
-    prompt = build_system_prompt(
+    prompt = build_agent_prompt(
         agent_type=AgentType.WORKER,
         llm_config=SystemAgentLLMConfig(),
-        user_context=_build_user_context(ai_language="zh-CN"),
-        now_utc=datetime.now(timezone.utc),
     )
 
-    assert "multiple short paragraphs" in prompt
+    assert "段间用\\n\\n" in prompt