refactor(server): plumb Arc<Settings> through workers and routes

Config sheds its 14 Bucket-B fields (retention, whisper, ollama, llm) and
gains a sibling Arc<Settings> in AppState, loaded from settings.toml at
startup via Settings::load_or_default. Workers (transcribe, analyze,
recovery, auto_trigger) and routes (health, bulk, case_actions,
user_web) take settings as a separate parameter or State<> extractor;
Config::llm_configured moves to Settings::llm_configured.

TestConfig::build_pair() returns (Arc<Config>, Arc<Settings>); the new
create_router_with_settings / create_router_and_session_store_with_settings
helpers wire both into integration tests that exercise LLM/Whisper/Ollama.
The legacy single-Arc create_router falls back to Settings::default()
so the 17 non-LLM tests stay untouched.

Verified: cargo build clean, clippy --all-targets clean, 318 tests pass.

server/tests/silent_case_empty_test.rs

@@ -55,10 +55,10 @@ async fn silent_only_case_settles_to_empty_without_llm_call() {
         .mount(&mock)
         .await;
 
-    let config = TestConfig::new()
+    let (_config, settings) = TestConfig::new()
         .with_data_path(data.path().to_path_buf())
         .with_ollama(mock.uri())
-        .build();
+        .build_pair();
 
     let vocab = Arc::new(Gazetteer::empty());
     let events_tx = events::channel();
@@ -77,7 +77,14 @@ async fn silent_only_case_settles_to_empty_without_llm_call() {
     };
 
     pipeline
-        .heal_orphans_if_idle(&user_root, slug, &http_client, &config, &vocab, &events_tx)
+        .heal_orphans_if_idle(
+            &user_root,
+            slug,
+            &http_client,
+            &settings,
+            &vocab,
+            &events_tx,
+        )
         .await;
 
     // Heal spawn drops the busy flag on completion — poll until idle.