refactor: rename bal-server-actix.rs to bal-server.rs

- Rename src/bin/bal-server-actix.rs -> src/bin/bal-server.rs
- Update Cargo.toml to point to new filename
- Update Dockerfile reference
- Update docs/08_security_audit.md references

Dockerfile

@@ -21,7 +21,7 @@ WORKDIR /build
 # Cache dependencies: copy Cargo.toml first, create dummy src to build deps
 COPY Cargo.toml Cargo.lock* ./
 RUN mkdir -p src/bin && \
-    echo 'fn main() {}' > src/bin/bal-server-actix.rs && \
+    echo 'fn main() {}' > src/bin/bal-server.rs && \
     echo 'fn main() {}' > src/bin/bal-pusher.rs && \
     echo '' > src/lib.rs && \
     echo '' > src/db.rs && \