perf: switch to uv for faster dependency installation

- Replace pip with uv in Dockerfile.service builder stage (~5-10x faster)
- Replace pip with uv in CI test step
- Separate pyproject.toml copy from source copy in Dockerfile for better
  Docker layer caching (deps only reinstalled when pyproject.toml changes)
- Add cache_from for buildx to reuse layers from previous builds
- Remove pip cache workaround from test step (not persisted in K8s)

docker/Dockerfile.service

@@ -1,6 +1,5 @@
 # Multi-stage Dockerfile for all Python microservices.
 # Build args:
-#   EXTRAS  — pip optional-dependency groups (e.g. "news", "sentiment,trading")
 #   SERVICE_MODULE — Python module name under services/ (e.g. "news_fetcher")
 
 # ---------------------------------------------------------------------------
@@ -10,16 +9,28 @@ FROM python:3.12-slim AS builder
 
 WORKDIR /app
 
-# Copy project metadata and source so pip can resolve the local package
+# Install uv for fast dependency resolution
+RUN pip install uv
+
+# Copy ONLY dependency metadata first — this layer is cached until
+# pyproject.toml changes, so dependency install is skipped on pure code changes.
 COPY pyproject.toml .
+
+# Create minimal package stubs so uv can resolve the local editable install
+# without copying all source (which would bust the cache on every commit).
+RUN mkdir -p shared services backtester && \
+    uv pip install --system --no-cache-dir ".[api,news,sentiment,trading,backtester]" && \
+    uv pip install --system --no-cache-dir curl_cffi 2>/dev/null || true
+
+# NOW copy the actual source code (changes here don't re-trigger dep install)
 COPY shared/ shared/
 COPY services/ services/
 COPY backtester/ backtester/
 COPY alembic/ alembic/
 COPY alembic.ini .
 
-# Install all service dependencies (hardcoded to avoid build-arg comma parsing issues)
-RUN pip install --no-cache-dir ".[api,news,sentiment,trading,backtester]" && pip install --no-cache-dir curl_cffi 2>/dev/null || true
+# Re-install in-place so the package metadata points to actual source
+RUN uv pip install --system --no-cache-dir --no-deps -e .
 
 # ---------------------------------------------------------------------------
 # Stage 2: slim runtime image