feat(web): 角色群像按定位配比生成（role_mix 缩减版）

- 契约: CharacterGenerateRequest 加 role_mix{定位:数量}，model_validator 归一
  count=各值之和（每项≥1、总和≤12），缺省退回单一 role+count
- @llm: build_character_gen_context/run_character_gen 加 role_mix 参并注入配比块
  （确定性、无时间戳，守 assemble 纯函数）；router 穿参
- character-gen.md 加"按配比严格分配 role"纪律 + regen prompt_hashes 金标准
- 前端: sanitizeRoleMix/roleMixTotal + buildCharacterGenerateRequest 第4参 +
  useCharacterGen 穿参 + RoleMixEditor + CharacterGenerator 单一/配比双模

apps/api/tests/test_generation_schema.py

@@ -0,0 +1,51 @@
+"""CharacterGenerateRequest.role_mix 校验单测（⑦ 群像按定位配比）。
+
+纯 pydantic 校验，无 DB/网关。契约：role_mix 在场时 count 取各值之和，
+每项数量须 ≥ 1、总和须 ≤ MAX_GENERATE_COUNT。
+"""
+
+from __future__ import annotations
+
+import pytest
+from pydantic import ValidationError
+from ww_api.schemas.generation import MAX_GENERATE_COUNT, CharacterGenerateRequest
+
+
+def test_role_mix_absent_keeps_explicit_count() -> None:
+    req = CharacterGenerateRequest(brief="剑修", count=3)
+    assert req.role_mix is None
+    assert req.count == 3
+
+
+def test_role_mix_sets_count_to_sum() -> None:
+    req = CharacterGenerateRequest(brief="群像", role_mix={"主角": 1, "对手": 2, "配角": 3})
+    assert req.count == 6
+
+
+def test_role_mix_overrides_provided_count() -> None:
+    # role_mix 在场时 count 取各值之和，忽略客户端显式传入的 count
+    req = CharacterGenerateRequest(brief="群像", count=1, role_mix={"主角": 2, "对手": 2})
+    assert req.count == 4
+
+
+def test_role_mix_total_at_max_allowed() -> None:
+    req = CharacterGenerateRequest(brief="群像", role_mix={"主角": MAX_GENERATE_COUNT})
+    assert req.count == MAX_GENERATE_COUNT
+
+
+def test_role_mix_sum_over_max_rejected() -> None:
+    with pytest.raises(ValidationError):
+        # 6 + 7 = 13 > 12
+        CharacterGenerateRequest(brief="群像", role_mix={"主角": 6, "对手": 7})
+
+
+def test_role_mix_empty_dict_rejected() -> None:
+    with pytest.raises(ValidationError):
+        CharacterGenerateRequest(brief="群像", role_mix={})
+
+
+def test_role_mix_nonpositive_value_rejected() -> None:
+    with pytest.raises(ValidationError):
+        CharacterGenerateRequest(brief="群像", role_mix={"主角": 0})
+    with pytest.raises(ValidationError):
+        CharacterGenerateRequest(brief="群像", role_mix={"主角": -1})