feat: 新增联系人标签查询功能

解析 contact.db 的 contact_label 表和 extra_buffer protobuf Field #30，
支持查询标签列表及指定标签下的成员。

- mcp_server.py: 新增 get_contact_tags / get_tag_members MCP 工具
- monitor_web.py: 新增 /api/tags JSON 端点，支持 ?name= 过滤

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

monitor_web.py

@@ -447,6 +447,96 @@ def load_contact_names():
     return names
 
 
+def _extract_pb_field_30(data):
+    """从 extra_buffer (protobuf) 中提取 Field #30 的字符串值（联系人标签ID）"""
+    if not data:
+        return None
+    pos = 0
+    n = len(data)
+    while pos < n:
+        tag = 0
+        shift = 0
+        while pos < n:
+            b = data[pos]; pos += 1
+            tag |= (b & 0x7f) << shift
+            if not (b & 0x80):
+                break
+            shift += 7
+        field_num = tag >> 3
+        wire_type = tag & 0x07
+        if wire_type == 0:
+            while pos < n and data[pos] & 0x80:
+                pos += 1
+            pos += 1
+        elif wire_type == 2:
+            length = 0; shift = 0
+            while pos < n:
+                b = data[pos]; pos += 1
+                length |= (b & 0x7f) << shift
+                if not (b & 0x80):
+                    break
+                shift += 7
+            if field_num == 30:
+                try:
+                    return data[pos:pos + length].decode('utf-8')
+                except Exception:
+                    return None
+            pos += length
+        elif wire_type == 1:
+            pos += 8
+        elif wire_type == 5:
+            pos += 4
+        else:
+            break
+    return None
+
+
+def load_contact_tags():
+    """加载联系人标签及其成员"""
+    try:
+        conn = sqlite3.connect(CONTACT_CACHE)
+        try:
+            label_rows = conn.execute(
+                "SELECT label_id_, label_name_, sort_order_ FROM contact_label ORDER BY sort_order_"
+            ).fetchall()
+        except Exception:
+            conn.close()
+            return []
+        if not label_rows:
+            conn.close()
+            return []
+
+        labels = {}
+        for lid, lname, sort_order in label_rows:
+            labels[lid] = {'id': lid, 'name': lname, 'sort_order': sort_order, 'members': []}
+
+        names = load_contact_names()
+        rows = conn.execute(
+            "SELECT username, extra_buffer FROM contact WHERE extra_buffer IS NOT NULL"
+        ).fetchall()
+        conn.close()
+
+        for username, buf in rows:
+            label_str = _extract_pb_field_30(buf)
+            if not label_str:
+                continue
+            display = names.get(username, username)
+            for lid_s in label_str.split(','):
+                try:
+                    lid = int(lid_s.strip())
+                except (ValueError, AttributeError):
+                    continue
+                if lid in labels:
+                    labels[lid]['members'].append({'username': username, 'display_name': display})
+
+        result = sorted(labels.values(), key=lambda t: t['sort_order'])
+        for t in result:
+            t['member_count'] = len(t['members'])
+        return result
+    except Exception:
+        return []
+
+
 def format_msg_type(t):
     return {
         1: '文本', 3: '图片', 34: '语音', 42: '名片',
@@ -1849,6 +1939,20 @@ class Handler(BaseHTTPRequestHandler):
             self.end_headers()
             self.wfile.write(data)
 
+        elif self.path.startswith('/api/tags'):
+            parsed = urllib.parse.urlparse(self.path)
+            params = urllib.parse.parse_qs(parsed.query)
+            name_filter = params.get('name', [''])[0].strip().lower()
+
+            tags = load_contact_tags()
+            if name_filter:
+                tags = [t for t in tags if name_filter in t['name'].lower()]
+
+            self.send_response(200)
+            self.send_header('Content-Type', 'application/json; charset=utf-8')
+            self.end_headers()
+            self.wfile.write(json.dumps(tags, ensure_ascii=False).encode('utf-8'))
+
         elif self.path == '/stream':
             self.send_response(200)
             self.send_header('Content-Type', 'text/event-stream')