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/components/generation/RoleMixEditor.tsx

@@ -0,0 +1,82 @@
+"use client";
+
+import { Plus, X } from "lucide-react";
+
+import { Button } from "@/components/ui/Button";
+import { TextInput } from "@/components/ui/TextInput";
+import {
+  MAX_CHARACTER_COUNT,
+  MIN_CHARACTER_COUNT,
+  roleMixTotal,
+  sanitizeRoleMix,
+} from "@/lib/generation/cards";
+
+// 单行配比：某定位 + 该定位要生成的数量。
+export interface RoleMixRow {
+  role: string;
+  count: number;
+}
+
+interface RoleMixEditorProps {
+  rows: RoleMixRow[];
+  onChange: (rows: RoleMixRow[]) => void;
+}
+
+// 群像按定位配比编辑器（⑦）：一组「定位 + 数量」行；合计封顶 MAX_CHARACTER_COUNT。
+// 不可变更新——每次编辑返回新数组，不改入参。
+export function RoleMixEditor({ rows, onChange }: RoleMixEditorProps) {
+  // 有效合计 = sanitize 后的总数（已按 MAX 截断），即实际会生成的张数。
+  const effectiveTotal = roleMixTotal(sanitizeRoleMix(rows));
+
+  const updateRow = (index: number, patch: Partial<RoleMixRow>): void => {
+    onChange(rows.map((r, i) => (i === index ? { ...r, ...patch } : r)));
+  };
+  const addRow = (): void => onChange([...rows, { role: "", count: 1 }]);
+  const removeRow = (index: number): void =>
+    onChange(rows.filter((_, i) => i !== index));
+
+  return (
+    <div className="flex flex-col gap-2" aria-label="角色定位配比">
+      {rows.map((row, i) => (
+        <div key={i} className="flex items-center gap-2">
+          <TextInput
+            value={row.role}
+            onChange={(e) => updateRow(i, { role: e.target.value })}
+            placeholder="定位：主角 / 对手 / 配角"
+            aria-label={`第 ${i + 1} 行定位`}
+            className="min-w-[10rem] flex-1"
+          />
+          <TextInput
+            type="number"
+            min={MIN_CHARACTER_COUNT}
+            max={MAX_CHARACTER_COUNT}
+            value={row.count}
+            onChange={(e) =>
+              updateRow(i, { count: Math.round(Number(e.target.value)) })
+            }
+            aria-label={`第 ${i + 1} 行数量`}
+            className="w-20"
+          />
+          <Button
+            variant="ghost"
+            size="icon"
+            onClick={() => removeRow(i)}
+            disabled={rows.length <= 1}
+            aria-label={`删除第 ${i + 1} 行`}
+          >
+            <X className="h-4 w-4" aria-hidden="true" />
+          </Button>
+        </div>
+      ))}
+      <div className="flex items-center justify-between">
+        <Button variant="outline" size="sm" onClick={addRow}>
+          <Plus className="h-4 w-4" aria-hidden="true" />
+          添加定位
+        </Button>
+        <span className="text-xs text-ink-soft">
+          合计 {effectiveTotal} / {MAX_CHARACTER_COUNT} 张
+        </span>
+      </div>
+    </div>
+  );
+}