chore(routing): flip LITELLM_BASE_URL default to https://llm-api.d-ma.be

Follow-up to infra#70. LiteLLM moved off piguard into k3s and the
public llm-api.d-ma.be hostname now upstreams to koala:30401. The
piguard:4000 default in the source bit-rots — works today because
piguard:4000 is still alive during the 7-day soak, breaks the moment
the compose comes down.

Pointing the default at the public hostname survives the cutover
without needing a follow-up. Production deploys via k3s already
override via env (in-cluster Service DNS) so this only affects local
dev shells without LITELLM_BASE_URL set.

- internal/config/routing.go: comment + envOr fallback
- internal/config/routing_test.go: expected value in defaults test
- scripts/smoke-routing.sh: shell default

task check: clean (tests + vet + govulncheck).

internal/config/routing_test.go

@@ -22,7 +22,7 @@ func TestLoadRoutingDefaults(t *testing.T) {
 	require.NoError(t, err)
 	assert.Equal(t, "3210", cfg.Port)
 	assert.Equal(t, "", cfg.MCPAuthToken)
-	assert.Equal(t, "http://piguard:4000", cfg.LiteLLMBaseURL)
+	assert.Equal(t, "https://llm-api.d-ma.be", cfg.LiteLLMBaseURL)
 	assert.Equal(t, "http://ingestion.supervisor:3300", cfg.BrainURL)
 	assert.Equal(t, "koala/qwen35-9b-fast", cfg.FastModel)
 	assert.Equal(t, "iguana/gemma4-26b", cfg.ThinkingModel)