arch: split ConfigRepository, extract polling, consolidate conversions, decouple protocol

- Value↔JSON: From impls on domain Value behind `json` feature, delete 4 duplicate converters
- ConfigRepository split into ConfigRepository (12), UserRepository (3), WidgetStateCache (2)
- polling orchestration moved from bootstrap to application::polling_service
- WidgetRenderer in client-domain owns scroll/cache, both clients use it
- network loop consolidated into client-application::run_connection_loop
- protocol crate drops domain dep, Wire↔Domain conversions move to adapters

Cargo.lock

@@ -79,9 +79,11 @@ dependencies = [
 name = "application"
 version = "0.1.0"
 dependencies = [
+ "anyhow",
  "domain",
  "thiserror",
  "tokio",
+ "tracing",
 ]
 
 [[package]]
@@ -526,6 +528,9 @@ dependencies = [
 [[package]]
 name = "domain"
 version = "0.1.0"
+dependencies = [
+ "serde_json",
+]
 
 [[package]]
 name = "dotenvy"
@@ -1687,7 +1692,6 @@ dependencies = [
 name = "protocol"
 version = "0.1.0"
 dependencies = [
- "domain",
  "postcard",
  "serde",
 ]