chore(deps): update ghcr.io/astral-sh/uv:latest docker digest to e590846

Author: renovate[bot]

backend/Dockerfile

@@ -48,7 +48,7 @@ RUN apt-get update \
 # Install uv (fast Python package installer)
 # Pin to specific version for reproducible builds
 # For SHA256 pinning: COPY --from=ghcr.io/astral-sh/uv@sha256:<digest> /uv /uvx /bin/
-COPY --from=ghcr.io/astral-sh/uv:latest@sha256:b1e699368d24c57cda93c338a57a8c5a119009ba809305cc8e86986d4a006754 /uv /uvx /bin/
+COPY --from=ghcr.io/astral-sh/uv:latest@sha256:e590846f4776907b254ac0f44b5b380347af5d90d668138ca7938d1b0c2f98d3 /uv /uvx /bin/
 
 # =============================================================================
 # Stage 2: Builder