fix: add Dockerfile logging and force unix line endings for Docker builds

The container build fails with 'unknown instruction: curl' on line 6, which
suggests the Dockerfile continuation characters or line endings may be
malformed. Add defensive logging to diagnose:

- Force newline='\n' in all write_text calls in build_image for consistent
  Unix line endings regardless of platform
- Log compiled Dockerfile and entrypoint content at INFO/DEBUG level
- Log Dockerfile byte count when written

This will let us see exactly what Docker is receiving in the next build attempt.

apps/api/src/services/docker_build.py

@@ -22,8 +22,9 @@ def build_image(instance_dir: str, dockerfile: str, tag: str, build_context: dic
 
     # Write Dockerfile
     dockerfile_path = Path(instance_dir) / "Dockerfile"
-    dockerfile_path.write_text(dockerfile)
-    logger.debug("Wrote Dockerfile to %s", dockerfile_path)
+    dockerfile_path.write_text(dockerfile, newline="\n")
+    logger.info("Wrote Dockerfile to %s (%d bytes)", dockerfile_path, len(dockerfile))
+    logger.debug("Dockerfile content:\n%s", dockerfile)
 
     # Write build context files
     if build_context:
@@ -37,7 +38,7 @@ def build_image(instance_dir: str, dockerfile: str, tag: str, build_context: dic
                 raise ValueError(f"Build context file path '{file_path}' escapes instance directory")
             
             full_path.parent.mkdir(parents=True, exist_ok=True)
-            full_path.write_text(content)
+            full_path.write_text(content, newline="\n")
             logger.debug("Wrote build context file: %s", full_path)
 
     # Build image