Scaffold Rust API and worker workspace

Pin the Rust toolchain and nextest profile so both service crates share a reproducible verification baseline.

crates/remora-api/src/lib.rs

@@ -0,0 +1,11 @@
+pub const COMPONENT_NAME: &str = "remora-api";
+
+#[cfg(test)]
+mod tests {
+    use super::COMPONENT_NAME;
+
+    #[test]
+    fn exposes_component_name() {
+        assert_eq!(COMPONENT_NAME, "remora-api");
+    }
+}