feat(dimentorin): AI agent RAG (embedding materi -> Qdrant + chat via 9router)

- ENV: AI_LLM_BASE_URL/API_KEY/MODEL, AI_EMBEDDING_MODEL (gemini-embedding-001), QDRANT_URL
- ai_agent module: chunking materi, embed_text + chat_completion (9router, SSE parse), Qdrant repo (dimentorin_materi collection, 3072d cosine)
- routes: POST /ai/chat (RAG answer + sources), POST /ai/materials/{id}/index, POST /ai/reindex
- e2e verified: reindex 3 chunks; chat 'ownership' -> materi Rust paling relevan 0.88; chat 'endpoint axum' -> materi Axum 0.82; jawaban gronding konteks

imphnen-dimentorin/src/ai_agent/domain/repository.rs

@@ -0,0 +1,25 @@
+use async_trait::async_trait;
+use uuid::Uuid;
+
+use super::rag_document::RagDocument;
+use imphnen_utils::AppError;
+
+#[async_trait]
+pub trait RagRepository: Send + Sync {
+	/// Upsert a document chunk into the vector store.
+	async fn upsert_document(
+		&self,
+		point_id: u64,
+		doc: &RagDocument,
+		embedding: Vec<f32>,
+	) -> Result<(), AppError>;
+	/// Search the vector store for the closest chunks to `embedding`.
+	async fn search(
+		&self,
+		embedding: Vec<f32>,
+		limit: u64,
+		material_id: Option<Uuid>,
+	) -> Result<Vec<(RagDocument, f32)>, AppError>;
+	/// Remove all chunks for a material (re-index support).
+	async fn delete_material(&self, material_id: Uuid) -> Result<(), AppError>;
+}