feat: better profile-based router assembly, tracing layer for responses with span-based request paths

Justfile

@@ -9,8 +9,8 @@ build-frontend:
     pnpm run -C web build
 
 # Auto-reloading backend server
-backend services=default_services:
-    bacon --headless run -- -- --services "{{services}}"
+backend *ARGS:
+    bacon --headless run -- -- {{ARGS}}
 
 # Production build
 build:
@@ -19,10 +19,10 @@ build:
 
 # Run auto-reloading development build with release characteristics (frontend is embedded, non-auto-reloading)
 # This is useful for testing backend release-mode details.
-dev-build services=default_services: build-frontend
-    bacon --headless run -- --profile dev-release -- --services "{{services}}" --tracing pretty
+dev-build *ARGS='--services web --tracing pretty': build-frontend
+    bacon --headless run -- --profile dev-release -- {{ARGS}}
 
 # Auto-reloading development build for both frontend and backend
 # Will not notice if either the frontend/backend crashes, but will generally be resistant to stopping on their own.
 [parallel]
-dev services=default_services: frontend (backend services)
+dev: frontend backend