fix: TUI now uses shared model router with auto-fallback support

The TUI was building its own ModelRouter with a duplicated client factory
that lacked auto same-model fallback, local_providers resolution, retry
config, and per-tier fallback logic. When Anthropic failed, it skipped
GitHub Models and fell straight to the local Ollama model.

Replace the duplicated ~50-line createClient + router setup in tui.ts
with a single call to the daemon's createModelRouter(), which already
handles all of these correctly. This removes ~50 lines of duplicated
code and ensures TUI and daemon have identical fallback behavior.

src/daemon/index.ts

@@ -175,7 +175,7 @@ export function createAutoFallbackClient(tierConfig: { provider: string; model:
   });
 }
 
-function createModelRouter(config: Config): ModelRouter {
+export function createModelRouter(config: Config): ModelRouter {
   const models = config.models;
 
   const defaultClient = createClientFromConfig(models.default);