fix(qr): lock QR code modules to black-on-white across all themes

AntD's <a-qrcode> defaults the module color to the active theme's
text token. Under the dark and ultra-dark themes that text is a light
gray, so the QR rendered low-contrast on the white canvas background
and phones could not lock onto it. Pinned color="#000000" and
bg-color="#ffffff" on every <a-qrcode> usage (share links in
QrPanel, 2FA enrollment in TwoFactorModal, sub/json/clash codes on
SubPage) so the contrast stays high regardless of panel theme.

frontend/src/pages/inbounds/QrPanel.vue

@@ -47,7 +47,7 @@ function download() {
     </div>
     <div v-if="showQr" class="qr-panel-canvas">
       <a-qrcode class="qr-code" :value="value" :size="size" type="svg" :bordered="false"
-        :title="t('copy')" @click="copy" />
+        color="#000000" bg-color="#ffffff" :title="t('copy')" @click="copy" />
     </div>
   </div>
 </template>

frontend/src/pages/settings/TwoFactorModal.vue

@@ -82,7 +82,7 @@ async function copyToken() {
       <p>{{ t('pages.settings.security.twoFactorModalFirstStep') }}</p>
       <div class="qr-wrap">
         <a-qrcode class="qr-code" :value="qrValue" :size="180" type="svg" :bordered="false"
-          error-level="L" :title="t('copy')" @click="copyToken" />
+          color="#000000" bg-color="#ffffff" error-level="L" :title="t('copy')" @click="copyToken" />
         <span class="qr-token">{{ token }}</span>
       </div>
       <a-divider />

frontend/src/pages/sub/SubPage.vue

@@ -204,7 +204,7 @@ const themeClass = computed(() => ({
                   <div class="qr-box">
                     <a-tag color="purple" class="qr-tag">{{ t('pages.settings.subSettings') }}</a-tag>
                     <a-qrcode class="qr-code" :value="subUrl" :size="QR_SIZE" type="svg" :bordered="false"
-                      :title="t('copy')" @click="copy(subUrl)" />
+                      color="#000000" bg-color="#ffffff" :title="t('copy')" @click="copy(subUrl)" />
                   </div>
                 </a-col>
                 <a-col v-if="subJsonUrl" :xs="24" :sm="12" class="qr-col">
@@ -213,14 +213,14 @@ const themeClass = computed(() => ({
                       {{ t('pages.settings.subSettings') }} JSON
                     </a-tag>
                     <a-qrcode class="qr-code" :value="subJsonUrl" :size="QR_SIZE" type="svg" :bordered="false"
-                      :title="t('copy')" @click="copy(subJsonUrl)" />
+                      color="#000000" bg-color="#ffffff" :title="t('copy')" @click="copy(subJsonUrl)" />
                   </div>
                 </a-col>
                 <a-col v-if="subClashUrl" :xs="24" :sm="12" class="qr-col">
                   <div class="qr-box">
                     <a-tag color="purple" class="qr-tag">Clash / Mihomo</a-tag>
                     <a-qrcode class="qr-code" :value="subClashUrl" :size="QR_SIZE" type="svg" :bordered="false"
-                      :title="t('copy')" @click="copy(subClashUrl)" />
+                      color="#000000" bg-color="#ffffff" :title="t('copy')" @click="copy(subClashUrl)" />
                   </div>
                 </a-col>
               </a-row>