refactor: reorganize project into monorepo with frontend scaffolding

Convert project from single backend to monorepo structure with separate
frontend (Vue 3 + TypeScript + Vite) and backend directories. Updates
all configuration files and build system to support both workspaces.

Ref: T007 (specs/001-modbus-relay-control)

backend/src/route/mod.rs

@@ -0,0 +1,37 @@
+//! API route handlers for the backend server.
+//!
+//! This module contains all the HTTP endpoint handlers organized by functionality:
+//! - Health checks
+//! - Application metadata
+
+use poem_openapi::Tags;
+
+mod health;
+mod meta;
+
+use crate::settings::Settings;
+
+#[derive(Tags)]
+enum ApiCategory {
+    Health,
+    Meta,
+}
+
+pub(crate) struct Api {
+    health: health::HealthApi,
+    meta: meta::MetaApi,
+}
+
+impl From<&Settings> for Api {
+    fn from(value: &Settings) -> Self {
+        let health = health::HealthApi;
+        let meta = meta::MetaApi::from(&value.application);
+        Self { health, meta }
+    }
+}
+
+impl Api {
+    pub fn apis(self) -> (health::HealthApi, meta::MetaApi) {
+        (self.health, self.meta)
+    }
+}