feat(core): bind request services and implement registered tasks

Wire plugin services through Bind/InjectFrom and AppContext so HTTP and
workers resolve dependencies after Apply. Register TaskHandler objects
with persisted results, and implement send_email_code, mail:send,
cleanup_inactive_users, and dispatch_bot_msg.

backend/docs/docs.go

@@ -5925,6 +5925,17 @@ const docTemplate = `{
                     "user"
                 ],
                 "summary": "发送邮箱验证码",
+                "parameters": [
+                    {
+                        "description": "目标邮箱",
+                        "name": "request",
+                        "in": "body",
+                        "required": true,
+                        "schema": {
+                            "$ref": "#/definitions/user.sendEmailCodeRequest"
+                        }
+                    }
+                ],
                 "responses": {
                     "200": {
                         "description": "发送成功",
@@ -5937,6 +5948,12 @@ const docTemplate = `{
                         "schema": {
                             "$ref": "#/definitions/response.Any"
                         }
+                    },
+                    "500": {
+                        "description": "发送失败",
+                        "schema": {
+                            "$ref": "#/definitions/response.Any"
+                        }
                     }
                 }
             }
@@ -8047,6 +8064,17 @@ const docTemplate = `{
                 }
             }
         },
+        "user.sendEmailCodeRequest": {
+            "type": "object",
+            "required": [
+                "email"
+            ],
+            "properties": {
+                "email": {
+                    "type": "string"
+                }
+            }
+        },
         "user.updateProfileRequest": {
             "type": "object",
             "properties": {