WiFi: select strongest signal when multiple APs with same SSID exist

[JinruiWang]

Summary

When remember_bssid_ is enabled and there are multiple APs with the same SSID (e.g., mesh network or dual-band router), connect to the one with the strongest signal instead of using the remembered BSSID which may have weaker signal.

Changes

include/wifi_station.h

Added has_multiple_same_ssid field to WifiApRecord struct to track if multiple APs with the same SSID were found during scan.

wifi_station.cc

HandleScanResult():

• Count how many APs with the same SSID name exist during scan
• Pass this info via has_multiple_same_ssid flag

StartConnect():

• If remember_bssid_ is enabled AND only one AP with this SSID exists → use remembered BSSID (original behavior)
• If remember_bssid_ is enabled AND multiple APs with same SSID exist → connect to strongest signal (new behavior)
• If remember_bssid_ is disabled → connect to strongest signal (unchanged)

Use Case

Useful for mesh networks or dual-band routers where you want to remember the WiFi credentials but always connect to the strongest available AP with that SSID.

[78]

对于当前的方案，如果 remember_bssid_ 是 false，esp-idf会动态管理当前连接的AP，并在掉线后自动切换到相同SSID的信号强的AP。当 remember_bssid_ 是 true时，会记住当前连接的AP，并在下次仍然连接该AP。

需要考虑一个问题，esp-idf第一轮拿到的AP列表，信号强度不一定准确，AP列表也不一定完整，有可能信号最强的那个AP并没有出现在第一次扫描的结果中。

[JinruiWang]

对于当前的方案，如果 remember_bssid_ 是 false，esp-idf会动态管理当前连接的AP，并在掉线后自动切换到相同SSID的信号强的AP。当 remember_bssid_ 是 true时，会记住当前连接的AP，并在下次仍然连接该AP。

需要考虑一个问题，esp-idf第一轮拿到的AP列表，信号强度不一定准确，AP列表也不一定完整，有可能信号最强的那个AP并没有出现在第一次扫描的结果中。

可能我理解的不够深刻。这是我这几天调试固件时碰到的问题，它总是在启动时连接到离我工位远的一个同名 ap 上，导致无法正常连接到我电脑上运行的 server，所以才有了这个 PR。

[78]

你需要的应该是：

1. 打开 rembember_bssid_
2. 删掉已经保存的ssid（因为它已记住远距离的AP了），重新添加