feat(web): add @memoh/icon package and unify brand icon system

Replace FontAwesome/CDN brand icons with local SVG-based Vue components
in a new shared @memoh/icon package. Provider icon URLs in conf/providers
YAML files are replaced with preset names, intercepted by ProviderIcon
component on the frontend. SearchProviderLogo and ChannelIcon components
are migrated to @memoh/icon. All icon containers now use a unified
circular gray (rounded-full bg-muted) style. Adds wechat and matrix
channel icons.

pnpm-lock.yaml

@@ -91,6 +91,9 @@ importers:
       '@fortawesome/vue-fontawesome':
         specifier: ^3.1.1
         version: 3.1.3(@fortawesome/fontawesome-svg-core@7.2.0)(vue@3.5.26(typescript@5.9.3))
+      '@memoh/icon':
+        specifier: workspace:*
+        version: link:../../packages/icons
       '@memoh/sdk':
         specifier: workspace:*
         version: link:../../packages/sdk
@@ -268,6 +271,16 @@ importers:
         specifier: ^5
         version: 5.9.3
 
+  packages/icons:
+    dependencies:
+      vue:
+        specifier: ^3.5.26
+        version: 3.5.26(typescript@5.9.3)
+    devDependencies:
+      tsx:
+        specifier: ^4.21.0
+        version: 4.21.0
+
   packages/sdk:
     dependencies:
       '@pinia/colada':