fix: DBAPI 类型补全 skill 相关方法签名

DBAPI 接口缺少 saveSkill/getAllSkills/deleteSkill/clearAllSkills/
searchSkills/incrementSkillUsage 六个方法的类型定义，
导致通过 bridge.db 调用技能相关方法时缺乏类型安全。

src/renderer/types.d.ts

@@ -431,6 +431,13 @@ export interface DBAPI {
   getTraces: (sessionId: string) => Promise<TraceEntry[]>;
   exportSessions: () => Promise<unknown>;
   importSessions: (data: unknown) => Promise<{ imported: number; skipped: number }>;
+  // v4.2 Skills
+  saveSkill: (skill: unknown) => Promise<{ success: boolean; id?: string; error?: string }>;
+  getAllSkills: () => Promise<unknown[]>;
+  deleteSkill: (id: string) => Promise<{ success: boolean; error?: string }>;
+  clearAllSkills: () => Promise<{ success: boolean; error?: string }>;
+  searchSkills: (query: string, limit?: number) => Promise<unknown[]>;
+  incrementSkillUsage: (id: string, success: boolean, durationMs: number) => Promise<{ success: boolean; error?: string }>;
 }
 
 // ── Window global 声明 ──