Add development setup guide + shared VS Code config

New docs/DEVELOPMENT-SETUP.md: clone-to-first-change onboarding
(Docker fast path, manual venv+Node daily driver, VS Code, the dev
loop, first-change pointer at the plugin lab, troubleshooting). Ship
.vscode/ launch/tasks/extensions so F5 debugs the backend on 5001 and
a task runs both servers; personal settings.json stays ignored. Fix
the README manual path - it ran the backend on the default 5000, but
the frontend dev server proxies to 5001, so nothing loaded; also add
the plugin upgrade-all step and a VS Code pointer.

README.md

@@ -148,11 +148,13 @@ pip install -r requirements.txt
 cp .env.example .env
 # Edit .env with your database credentials and secrets.
 
+export FLASK_APP=shopdb
 flask db upgrade
+flask plugin upgrade-all      # per-plugin schema (ADR-008)
 flask seed permissions
 flask seed settings
 flask seed reference-data
-flask run
+flask run --port 5001         # MUST be 5001 - the frontend dev server proxies here
 
 # Frontend (separate terminal)
 cd frontend
@@ -162,7 +164,10 @@ npm run build        # production build into frontend/dist (served by Flask)
 ```
 
 Complete first-run setup at `/setup`, or run `flask seed admin` for a headless
-admin account.
+admin account. The repo ships VS Code config in `.vscode/` (F5 debugs the
+backend; a "Dev site" task runs both servers). A fuller day-one walkthrough,
+including VS Code and troubleshooting, is the DEVELOPMENT-SETUP page in the
+project wiki.
 
 To import a site's legacy data, use the HTTP import surface: an admin API
 token plus [docs/IMPORT-API.md](docs/IMPORT-API.md) drive the whole migration