fix: M4 Phase 1 bugs - dev.chunks refs, search_path, uuid column

Bug fixes from M4 report:
- 4 remaining dev.chunks → dev.chunk in SQL queries
- search_path includes public for pgvector extension
- get_chunk_by_chunk_id_and_uuid: uuid → file_uuid
- New endpoint: GET /api/v1/file/:uuid/chunk/:chunk_id

src/api/server.rs

@@ -1306,6 +1306,25 @@ async fn trigger_processing(
     })))
 }
 
+async fn get_chunk_by_path(
+    Path((file_uuid, chunk_id)): Path<(String, String)>,
+    State(state): State<AppState>,
+) -> Result<Json<Chunk>, StatusCode> {
+    let chunk = state
+        .db
+        .get_chunk_by_chunk_id_and_uuid(&chunk_id, &file_uuid)
+        .await
+        .map_err(|_| {
+            tracing::error!("[get_chunk_by_path] DB error: {}:{}", file_uuid, chunk_id);
+            StatusCode::INTERNAL_SERVER_ERROR
+        })?
+        .ok_or_else(|| {
+            tracing::warn!("[get_chunk_by_path] Not found: {}:{}", file_uuid, chunk_id);
+            StatusCode::NOT_FOUND
+        })?;
+    Ok(Json(chunk))
+}
+
 async fn get_asset_status(
     State(state): State<AppState>,
     Path(uuid): Path<String>,
@@ -2508,6 +2527,7 @@ pub async fn start_server(host: &str, port: u16) -> anyhow::Result<()> {
         .route("/api/v1/files/scan", get(scan_files))
         .route("/api/v1/file/:file_uuid/probe", get(probe_by_uuid))
         .route("/api/v1/file/:file_uuid/process", post(trigger_processing))
+        .route("/api/v1/file/:file_uuid/chunk/:chunk_id", get(get_chunk_by_path))
 
         .route("/api/v1/progress/:uuid", get(get_progress))
         .route("/api/v1/jobs", get(list_jobs))