chore: unify dev setup with concurrently

Adds concurrently to start both the Vite frontend and Hono backend simultaneously in one terminal via the `bun run dev` command. Also updates documentation in README.md and CLAUDE.md to reflect the new development workflow.

CLAUDE.md

@@ -9,7 +9,8 @@ GearBox is a single-user web app for managing gear collections (bikepacking, sim
 ## Commands
 
 ```bash
-# Development (run both in separate terminals)
+# Development
+bun run dev                 # Starts both Vite client (:5173) and Hono server (:3000) concurrently
 bun run dev:client          # Vite dev server on :5173 (proxies /api to :3000)
 bun run dev:server          # Hono server on :3000 with hot reload
 
@@ -67,4 +68,4 @@ bun run build               # Vite build → dist/client/
 - **Thread resolution**: Resolving a thread copies the winning candidate's data into a new item in the collection, sets `resolvedCandidateId`, and changes status to "resolved".
 - **Setup item sync**: `PUT /api/setups/:id/items` replaces all setup_items atomically (delete all, re-insert).
 - **Image uploads**: `POST /api/images` saves to `./uploads/` with UUID filename, returned as `imageFilename` on item/candidate records.
-- **Aggregates** (weight/cost totals): Computed via SQL on read, not stored on records.
+- **Aggregates** (weight/cost totals): Computed via SQL on read, not stored on records.