fix: make Docker container UID/GID configurable

Add UID and GID build arguments to Dockerfiles to allow matching the
container user to the host user. This fixes file permission issues when
mounting host directories as volumes.

Default remains 1001 for backward compatibility. To match host user:
  UID=$(id -u) GID=$(id -g) docker-compose build

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

Dockerfile

@@ -59,6 +59,11 @@ FROM node:22-slim AS server
 ARG GIT_COMMIT_SHA=unknown
 LABEL automaker.git.commit.sha="${GIT_COMMIT_SHA}"
 
+# Build arguments for user ID matching (allows matching host user for mounted volumes)
+# Override at build time: docker build --build-arg UID=$(id -u) --build-arg GID=$(id -g) ...
+ARG UID=1001
+ARG GID=1001
+
 # Install git, curl, bash (for terminal), gosu (for user switching), and GitHub CLI (pinned version, multi-arch)
 RUN apt-get update && apt-get install -y --no-install-recommends \
     git curl bash gosu ca-certificates openssh-client \
@@ -79,8 +84,10 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
 RUN npm install -g @anthropic-ai/claude-code
 
 # Create non-root user with home directory BEFORE installing Cursor CLI
-RUN groupadd -g 1001 automaker && \
-    useradd -u 1001 -g automaker -m -d /home/automaker -s /bin/bash automaker && \
+# Uses UID/GID build args to match host user for mounted volume permissions
+# Use -o flag to allow non-unique IDs (GID 1000 may already exist as 'node' group)
+RUN groupadd -o -g ${GID} automaker && \
+    useradd -o -u ${UID} -g automaker -m -d /home/automaker -s /bin/bash automaker && \
     mkdir -p /home/automaker/.local/bin && \
     mkdir -p /home/automaker/.cursor && \
     chown -R automaker:automaker /home/automaker && \