fix: prevent duplicate login profiles in dropdown

When users log out and log back in with the same profile, the profile
was being added to the profiles array again, causing duplicates in
the dropdown menu. 

This change modifies the login action to check if a profile with the
same ID already exists before adding it. If it exists, the profile
is updated instead of creating a duplicate entry.

Fixes duplicate profile issue reported in PR comments.

Co-authored-by: Anguel <modelorona@users.noreply.github.com>

Author: claude[bot]

frontend/src/store/auth.ts

@@ -41,7 +41,17 @@ export const authSlice = createSlice({
         ...(action.payload as LoginCredentials),
       }
       state.current = profile as LocalLoginProfile;
-      state.profiles.push(profile as LocalLoginProfile);
+      
+      // Check if profile already exists to prevent duplicates
+      const existingProfileIndex = state.profiles.findIndex(p => p.Id === profile.Id);
+      if (existingProfileIndex >= 0) {
+        // Update existing profile instead of adding duplicate
+        state.profiles[existingProfileIndex] = profile as LocalLoginProfile;
+      } else {
+        // Add new profile
+        state.profiles.push(profile as LocalLoginProfile);
+      }
+      
       state.status = "logged-in";
     },
     switch: (state, action: PayloadAction<{id: string}>) => {