chore: add bacon config and improve dev workflow

- Add bacon.toml for Rust development watching with keybindings
- Update Justfile to use bacon for dev watching
- Configure frontend to build to ./public for backend serving
- Improve Justfile organization with comments and better task separation
- Add dev-backend and dev-frontend tasks for separate workflows
- Minor formatting fix in backend/src/state.rs

frontend/astro.config.mjs

@@ -20,6 +20,7 @@ if (
 // https://astro.build/config
 
 export default defineConfig({
+  outDir: "../public",
   build: {
     assets: "assets",
   },