feat: IMAP mail sync with thread-to-contact matching (PRD §6.1)

Real IMAP connection via imapflow library:
- Connects to IMAP server (IMAPFlow, TLS on port 993)
- Fetches recent messages (configurable limit, default 20)
- Extracts: from, fromEmail, subject, date, snippet (200 chars)
- Thread-to-contact matching (PRD §6.1):
  1. Match sender email against persons table
  2. If no person match, extract domain and match against company.website
  3. Returns matchedCompany + matchedPerson for each email
- Audit-logged (action: crm.mailsync:imap)
- Zod validated (host, port, user, password, folder, limit)
- 502 on IMAP connection failure with detail
- 400 on validation failure

Tested: invalid creds → 502 'IMAP connection failed', missing host → 400

skills/gaokao-fetch-volunteers/examples/api_request_shandong.json

@@ -0,0 +1,19 @@
+{
+  "province": "山东",
+  "classify": "综合",
+  "subjects": "物理,化学,生物",
+  "gradeType": null,
+  "score": 650,
+  "rank": null,
+  "batch": "本科批",
+  "universitys": "北京航空航天大学,华东师范大学,中山大学",
+  "provinces": "北京,上海,广东,湖北",
+  "tags": "985,211,双一流",
+  "majorClass": "计算机类,电子信息类,自动化类,临床医学类",
+  "universityNum": 30,
+  "majorNum": 6,
+  "isAdjust": true,
+  "volunteerType": "ACADEMY_GROUP",
+  "returnUniversityNum": 30,
+  "intentionNum": 0
+}

skills/gaokao-fetch-volunteers/examples/api_request_template.json

@@ -0,0 +1,19 @@
+{
+  "province": "北京",
+  "classify": "综合",
+  "subjects": "物理,化学,生物",
+  "gradeType": "本科",
+  "score": 650,
+  "rank": null,
+  "batch": "本科批",
+  "universitys": null,
+  "provinces": null,
+  "tags": null,
+  "majorClass": null,
+  "universityNum": 30,
+  "majorNum": 6,
+  "isAdjust": true,
+  "volunteerType": "ACADEMY_GROUP",
+  "returnUniversityNum": 30,
+  "intentionNum": 0
+}