feat: initialize rust backend with axum server, seaorm models, and project scaffolding

backend/src/models/bio/mod.rs

@@ -0,0 +1,7 @@
+//! Biomarker entities for health data tracking.
+
+pub mod biomarker_entry;
+pub mod biomarker_type;
+
+pub use biomarker_entry::Entity as BiomarkerEntry;
+pub use biomarker_type::Entity as BiomarkerType;