fix: use nm_utils_ssid_to_utf8 for SSID decoding in AccessPoint

[caixr23]

Root Cause Analysis

The SSID decoding in AccessPointPrivate::propertiesChanged() was hardcoded to QString::fromUtf8(rawSsid). For SSIDs encoded with GBK/GB2312 (common in Chinese network environments), this produced garbled text in the network list. The rawSsid (QByteArray) was stored correctly, but the ssid (QString) used for display was incorrectly decoded.

Key evidence:

• accesspoint.cpp line 199 (before fix): ssid = QString::fromUtf8(rawSsid) — hardcoded UTF-8, no fallback
• Only AccessPoint::ssid() (returns QString) was affected; WirelessSetting::ssid() (returns QByteArray) was not
• The deepin fork networkmanager-qt6 had no modifications to this code — identical to upstream KDE

Fix

Replace the hardcoded QString::fromUtf8(rawSsid) with nm_utils_ssid_to_utf8() from libnm, consistent with how nmtui decodes SSIDs:

1. Add #include <libnm/NetworkManager.h> to accesspoint.cpp
2. Call nm_utils_ssid_to_utf8() to decode the raw SSID bytes to a UTF-8 string
3. Convert the C string to QString via QString::fromUtf8() and free with g_free()

nm_utils_ssid_to_utf8() handles encoding detection:

• Validates UTF-8 and returns directly if valid
• Falls back to locale-aware encoding detection (including GBK/GB2312 for zh_CN locale)
• Falls back to ISO-8859-1 as last resort

This is complementary to dde-network-core PR #627, which handles the display and save paths at the DDE layer. Both fixes can be merged independently.

Safety Assessment

• Risk level: Low
• UTF-8 encoded SSIDs are decoded correctly (nm_utils_ssid_to_utf8 validates UTF-8 first)
• Non-UTF-8 SSIDs are decoded using the same function as nmtui, ensuring consistent behavior
• No new dependencies — libnm is already a REQUIRED PUBLIC dependency of networkmanager-qt6
• rawSsid() and other APIs are completely unaffected

Test Suggestion

• Verify UTF-8 encoded SSID networks still display correctly (no regression)
• Verify GBK encoded SSID networks now display correctly instead of garbled text
• Verify ssidChanged signal carries correct value for both encodings

---

根因分析

AccessPointPrivate::propertiesChanged() 中 SSID 解码硬编码为 QString::fromUtf8(rawSsid)，对 GBK/GB2312 编码的 SSID 产生乱码。

修复方案

使用 libnm 的 nm_utils_ssid_to_utf8() 替换硬编码的 fromUtf8，与 nmtui 的 SSID 解码方式保持一致。nm_utils_ssid_to_utf8() 会先验证 UTF-8，失败时根据 locale 回退到对应编码（如 zh_CN 下尝试 GBK/GB2312），最后回退 ISO-8859-1。

libnm 已是 networkmanager-qt6 的 REQUIRED PUBLIC 依赖，无需新增依赖。

与 dde-network-core PR #627 互补，两者可分别合入。

安全评估

• 风险等级：低
• UTF-8 编码 SSID 走相同的验证路径（零行为变更）
• 非 UTF-8 SSID 使用与 nmtui 相同的解码逻辑
• libnm 已是现有依赖，无新增依赖

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[mhduiy]

问题不复现，中间版本已经修复了