docs: 授权延长在 README 里单独成节，主界面与动图带上延长申请

- 「申请延长」单独成节：同事端 ④⑤⑥ 与 App 的连接与授权截图放在一起，
  写明卡片提示、点「批准延长」选时长、最近结束的设备也可直接延长
- 演示数据：MySQL 通道带一条延长申请和一台最近结束的设备，主界面、动图、
  授权管理与网页面板展示同一组数据，卡片上能看到「申请延长 1」

tools/ui-snapshots/webpanel/main.go

@@ -96,8 +96,11 @@ func main() {
 		  "metrics":{"tunnel_id":"t1","status":"online","active_conns":3,"total_conns":1287,"bytes_in":245039104,"bytes_out":8703180,"blocked_attempts":12,
 		    "dynamic_leases":[{"ip":"192.168.1.21","expires_at":%q,"name":"张三","invite":"a1","duration":"2h","started_at":%q},
 		                      {"ip":"192.168.1.35","expires_at":%q,"name":"王小明","invite":"a2","duration":"8h","awaiting_connect":true}],
-		    "pending":[{"id":"r1","tunnel_id":"t1","name":"李四","ip":"192.168.1.88","invite":"a3","at":%q,"status":"pending"}]}}`,
-			at(-3725), at(10675), at(-3300), at(7000), at(-200), at(80000), at(-60)),
+		    "pending":[{"id":"r1","tunnel_id":"t1","name":"李四","ip":"192.168.1.88","invite":"a3","at":%q,"status":"pending"}]},
+		  "renewals":[{"tunnel_id":"t1","ip":"192.168.1.47","name":"赵六","invite":"ab1","ended_at":%q,"renew_before":%q,
+		    "request":{"id":"rn1","tunnel_id":"t1","name":"赵六","ip":"192.168.1.47","invite":"ab1","at":%q,"status":"pending","renewal":true}},
+		    {"tunnel_id":"t1","ip":"192.168.1.36","name":"王五","invite":"ab2","ended_at":%q,"renew_before":%q}]}`,
+			at(-3725), at(10675), at(-3300), at(7000), at(-200), at(80000), at(-60), at(-1200), at(6000), at(-60), at(-3000), at(4200)),
 		member("g1a", "10.0.3.11", 33670, 1, -1500, 1320, 3203180, 18039104),
 		member("g1b", "10.0.3.12", 33671, 2, -1400, 1100, 2203180, 12039104),
 		member("g1c", "10.0.3.13", 33672, 0, 0, 0, 0, 0),