feat: add cache toggle, unregister API and chunk training docs

- Add POST /api/v1/config/cache for cache toggle
- Add POST /api/v1/unregister for video deletion
- Add CHUNK_DATA_STRUCTURE.md for marcom training
- Fix processor_results query in delete_video

src/core/config.rs

@@ -1,5 +1,23 @@
 use once_cell::sync::Lazy;
 use std::env;
+use std::sync::RwLock;
+
+pub static RUNTIME_CACHE_ENABLED: Lazy<RwLock<bool>> = Lazy::new(|| {
+    let initial = env::var("MONGODB_CACHE_ENABLED")
+        .unwrap_or_else(|_| "true".to_string())
+        .parse()
+        .unwrap_or(true);
+    RwLock::new(initial)
+});
+
+pub fn get_cache_enabled() -> bool {
+    *RUNTIME_CACHE_ENABLED.read().unwrap()
+}
+
+pub fn set_cache_enabled(enabled: bool) {
+    *RUNTIME_CACHE_ENABLED.write().unwrap() = enabled;
+    tracing::info!("Cache enabled set to: {}", enabled);
+}
 
 pub static DATABASE_URL: Lazy<String> = Lazy::new(|| {
     env::var("DATABASE_URL")