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/identity_agent_api.rs

@@ -9,7 +9,7 @@ use serde::{Deserialize, Serialize};
 use sqlx::Row;
 use std::path::PathBuf;
 
-use crate::api::server::AppState;
+use crate::api::types::AppState;
 use crate::core::db::schema;
 use crate::core::db::PostgresDb;