perf: improve Docker layer caching for faster builds

Split dependency installation from source copy:
1. Copy manifests first (pyproject.toml, uv.lock)
2. Install deps with --no-install-project (cached layer)
3. Copy source code
4. Install project with --no-deps (fast)

This ensures source code changes don't invalidate the expensive
~2GB dependency installation layer.

Author: namastex888

Dockerfile

@@ -15,12 +15,17 @@ RUN uv python install 3.12 && uv venv /app/.venv --python 3.12
 ENV VIRTUAL_ENV=/app/.venv
 ENV PATH="/app/.venv/bin:$PATH"
 
-# Copy project files for reproducible install
+# Copy manifests first to leverage layer caching
 COPY pyproject.toml uv.lock ./
+
+# Install dependencies from lock file (cached unless deps change)
+RUN uv sync --frozen --no-dev --no-install-project
+
+# Copy source code (changes here don't invalidate dep cache)
 COPY src/ ./src/
 
-# Install with frozen lock file (reproducible builds)
-RUN uv sync --frozen --no-dev
+# Install the project itself (fast, no deps to resolve)
+RUN uv pip install --no-deps .
 
 # Runtime config
 RUN mkdir -p /app/data