Downgrade home crate for Rust 1.85 compatibility

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

backend_rust/Dockerfile

@@ -22,6 +22,9 @@ COPY migration/Cargo.toml ./migration/
 RUN mkdir src && echo "fn main() {}" > src/main.rs
 RUN mkdir -p migration/src && echo "fn main() {}" > migration/src/main.rs && echo "" > migration/src/lib.rs
 
+# Downgrade home crate to version compatible with Rust 1.85
+RUN cargo update home@0.5.12 --precise 0.5.9 || true
+
 # Build dependencies only
 RUN cargo build --release