feat(agent): 添加视频创作工作流技能系统和流程工具

新增基于 SKILL.md 的视频创作工作流系统，Agent 可通过 skills 目录加载结构化的导演指令；实现 validate_storyboard、update_manifest_items、confirm_images 三个流程工具支撑分镜校验、提示词更新和图片确认。

web/server/agent/pi-bridge.ts

@@ -3,6 +3,9 @@ import type { AgentEvent } from '@earendil-works/pi-agent-core';
 import { streamSimple } from '@earendil-works/pi-ai';
 import type { AssistantMessage } from '@earendil-works/pi-ai';
 import { WebSocket } from 'ws';
+import fs from 'fs';
+import path from 'path';
+import { fileURLToPath } from 'url';
 import { createPiModel } from './pi-model';
 import { createPiTools } from './pi-tools';
 import { tools } from './tools/index';
@@ -10,6 +13,32 @@ import { videoAgent } from './index';
 import { dbToPiMessages, saveUserMessage, saveAssistantMessage, saveToolResult, type DbMessage } from './pi-persist';
 import { getDb } from '../db';
 
+const __filename = fileURLToPath(import.meta.url);
+const __dirname = path.dirname(__filename);
+const SKILLS_DIR = path.join(__dirname, 'skills');
+
+function loadSkills(): string {
+  const parts: string[] = [];
+  if (!fs.existsSync(SKILLS_DIR)) return '';
+
+  const skillDirs = fs.readdirSync(SKILLS_DIR, { withFileTypes: true })
+    .filter((d) => d.isDirectory());
+
+  for (const dir of skillDirs) {
+    const skillFile = path.join(SKILLS_DIR, dir.name, 'SKILL.md');
+    if (fs.existsSync(skillFile)) {
+      let content = fs.readFileSync(skillFile, 'utf-8');
+      // Strip YAML frontmatter
+      content = content.replace(/^---[\s\S]*?---\n*/, '');
+      parts.push(content.trim());
+    }
+  }
+
+  return parts.join('\n\n---\n\n');
+}
+
+const cachedSkillContent = loadSkills();
+
 interface RunContext {
   currentAssistantMsgId: string | null;
 }
@@ -35,7 +64,7 @@ export async function runAgentChat(ws: WebSocket, convId: string, userContent: s
 
   const agent = new Agent({
     initialState: {
-      systemPrompt: videoAgent.getSystemPrompt(),
+      systemPrompt: videoAgent.getSystemPrompt() + (cachedSkillContent ? '\n\n' + cachedSkillContent : ''),
       model,
       thinkingLevel: 'off',
       tools: piTools,