refactor: modularize server.rs into separate route modules

- Extract scan.rs, files.rs, types.rs, processing.rs, visual_chunk_search.rs
- Move AppState and AppConfig to types.rs
- Each module exposes pub fn xxx_routes() -> Router<AppState>
- server.rs reduced from 5005 to 118 lines (orchestrator only)
- All stubs filled with real implementations from git history
- Verify: cargo check, clippy, tests all pass

src/api/search.rs

@@ -51,7 +51,7 @@ pub struct SmartSearchResponse {
 // --- API Handler ---
 
 pub async fn smart_search(
-    State(state): State<crate::api::server::AppState>,
+    State(state): State<crate::api::types::AppState>,
     Json(req): Json<SmartSearchRequest>,
 ) -> Result<Json<SmartSearchResponse>, (StatusCode, Json<serde_json::Value>)> {
     let db = &state.db;
@@ -126,6 +126,6 @@ pub async fn smart_search(
 
 // --- Router Setup ---
 
-pub fn search_routes() -> Router<crate::api::server::AppState> {
+pub fn search_routes() -> Router<crate::api::types::AppState> {
     Router::new().route("/api/v1/search/smart", post(smart_search))
 }