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/web/lib/generation/useCharacterGen.ts

@@ -21,6 +21,8 @@ export interface CharacterGenInput {
   brief: string;
   count: number;
   role?: string | null;
+  // 群像按定位配比（⑦）；在场时后端把 count 定为各值之和，忽略 count/role。
+  roleMix?: Readonly<Record<string, number>> | null;
 }
 
 export interface UseCharacterGen {
@@ -50,7 +52,7 @@ export function useCharacterGen(): UseCharacterGen {
   const toast = useToast();
 
   const generate = useCallback<UseCharacterGen["generate"]>(
-    async ({ projectId, brief, count, role }) => {
+    async ({ projectId, brief, count, role, roleMix }) => {
       setGenStatus("generating");
       setCards([]);
       setConflicts(null);
@@ -60,7 +62,7 @@ export function useCharacterGen(): UseCharacterGen {
           "/projects/{project_id}/characters/generate",
           {
             params: { path: { project_id: projectId } },
-            body: buildCharacterGenerateRequest(brief, count, role),
+            body: buildCharacterGenerateRequest(brief, count, role, roleMix),
           },
         );
         if (error || !data) {