feat: Mode C pipeline end-to-end (lexical + tags + fusion)

Implement Pipeline::load/suggest for Mode C: lexical search per segment,
cross-segment dedup via fusion, tag derivation, filter application.
Add meta_lookup fallback (exact → strip trailing 0 → 3-char root) to
bridge the ICD code granularity gap between the corpus (E11.90-style
6-char codes) and ClaML (which only stores E11, E11.0-style entries).

tests/pipeline_mode_c_tests.rs

@@ -0,0 +1,27 @@
+use alpha_id::pipeline::Pipeline;
+use alpha_id::model::{Config, Filter, Mode};
+
+fn cfg() -> Config {
+    Config::load("config/default.toml").unwrap()
+}
+
+#[test]
+fn mode_c_end_to_end_real_data() {
+    let p = Pipeline::load(&cfg()).unwrap();
+    let dictation = "Patient mit Diabetes mellitus Typ 2\n\nArterielle Hypertonie";
+    let res = p.suggest(dictation, Mode::C, &Filter::default(), 10);
+    assert!(!res.suggestions.is_empty());
+    assert!(res.suggestions.len() <= 10);
+    assert!(res.suggestions.iter().any(|s| s.icd_code.starts_with("E11")));
+    assert!(res.suggestions.iter().any(|s| s.icd_code.starts_with("I10")));
+    assert_eq!(res.diagnostics.segment_count, 2);
+    assert_eq!(res.diagnostics.mode, "C");
+}
+
+#[test]
+fn billable_only_filter_excludes_three_digit_v_codes() {
+    let p = Pipeline::load(&cfg()).unwrap();
+    let f = Filter { billable_only: true, valid_only: true, chapters: None, exclude_exotic: false };
+    let res = p.suggest("Cholera", Mode::C, &f, 10);
+    assert!(res.suggestions.iter().all(|s| s.tags.billable && s.tags.valid));
+}