perf: optimize Dockerfile with layer caching for faster rebuilds

Dockerfile

@@ -2,15 +2,26 @@ FROM python:3.10
 
 WORKDIR /home/user/app
 
-# Copy application files FIRST
-COPY . .
-
-# Install system dependencies
+# Install system dependencies (cached layer)
 RUN apt-get update && apt-get install -y ffmpeg && rm -rf /var/lib/apt/lists/*
 
-# Install Python dependencies including the package itself
-RUN pip install --no-cache-dir -r requirements.txt && \
-    pip install --no-cache-dir -e .
+# Copy only requirements first (cached if unchanged)
+COPY requirements.txt .
+
+# Install Python dependencies (cached layer)
+RUN pip install --no-cache-dir -r requirements.txt
+
+# Copy setup files needed for package install
+COPY setup.py pyproject.toml ./
+
+# Copy source code
+COPY src ./src
+
+# Install the package in editable mode
+RUN pip install --no-cache-dir -e .
+
+# Copy the rest of the application
+COPY . .
 
 # Expose Gradio port
 EXPOSE 7860