refactor(backend): alihkan Memory ke zesdex-cms MarkdownMemoryRepository

Ganti semua pemanggilan Memory::read/write/remove/list di zesdex-backend
dengan MarkdownMemoryRepository dari zesdex-cms. Hapus re-export
model::memory yang sudah tidak dipakai.

Method mapping: read -> load, write -> save, remove -> delete, list -> list.
Import trait MemoryRepository untuk method resolution.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

crates/zesdex-backend/src/app/mode/learning.rs

@@ -1,4 +1,5 @@
 use crate::app::state::rest::AppStateRest;
+use zesdex_cms::domain::repository::MemoryRepository;
 
 /// A unified representation of a lesson item for the interactive TUI overlay.
 #[derive(Debug, Clone)]
@@ -53,9 +54,9 @@ pub fn get_learning_items(state: &AppStateRest) -> Vec<LearningItem> {
     }
 
     // 2. Load stored memory lessons from long-term memory directory
-    let names = crate::model::memory::Memory::list(&state.memory_dir);
+    let names = zesdex_cms::infrastructure::persistence::memory_repo::MarkdownMemoryRepository::new().list(&state.memory_dir).unwrap_or_default();
     for name in names {
-        if let Ok(mem) = crate::model::memory::Memory::read(&state.memory_dir, &name) {
+        if let Ok(mem) = zesdex_cms::infrastructure::persistence::memory_repo::MarkdownMemoryRepository::new().load(&state.memory_dir, &name) {
             if mem.kind == "lesson" {
                 items.push(LearningItem::Stored {
                     name: mem.name,