Fix: Use npm install instead of npm ci for version flexibility

npm ci fails when vitest@4.x peer dep (vite@7.x) doesn't match
locked vite@5.x. Using npm install --legacy-peer-deps resolves this.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Dockerfile

@@ -9,8 +9,8 @@ WORKDIR /frontend
 # Copy package files first for better caching
 COPY frontend/package.json frontend/package-lock.json ./
 
-# Install dependencies
-RUN npm ci
+# Install dependencies (use npm install to resolve version mismatches)
+RUN npm install --legacy-peer-deps
 
 # Copy frontend source code
 COPY frontend/ ./