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/agent_api.rs

@@ -2,7 +2,7 @@ use axum::{extract::State, http::StatusCode, response::Json, routing::post, Rout
 use reqwest::Client;
 use serde::{Deserialize, Serialize};
 
-use crate::api::server::AppState;
+use crate::api::types::AppState;
 
 pub fn agent_routes() -> Router<AppState> {
     Router::new().route("/api/v1/agents/translate", post(translate_text))