feat: Mode A hybrid pipeline with graceful degradation to C

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/pipeline_mode_a_tests.rs

@@ -0,0 +1,13 @@
+use alpha_id::pipeline::Pipeline;
+use alpha_id::model::{Config, Filter, Mode};
+
+#[test]
+fn mode_a_degrades_to_c_when_ionos_unreachable() {
+    let mut cfg = Config::load("config/default.toml").unwrap();
+    cfg.ionos_base_url = "http://127.0.0.1:1".into(); // refused
+    let p = Pipeline::load(&cfg).unwrap();
+    let res = p.suggest("Diabetes mellitus Typ 2", Mode::A, &Filter::default(), 10);
+    assert!(res.diagnostics.degraded);                 // fell back
+    assert!(!res.suggestions.is_empty());              // still answered
+    assert!(res.suggestions.iter().any(|s| s.icd_code.starts_with("E11")));
+}