Add development setup guide and shared VS Code config

Clone-to-first-change onboarding, plus .vscode launch/tasks/extensions
so F5 debugs the backend and a task runs both dev servers. Fix the
README manual path to run the backend on 5001 (the frontend proxies
there; the default 5000 loaded nothing).

.vscode/extensions.json

@@ -0,0 +1,9 @@
+{
+  "recommendations": [
+    "ms-python.python",
+    "ms-python.vscode-pylance",
+    "Vue.volar",
+    "dbaeumer.vscode-eslint",
+    "ms-azuretools.vscode-docker"
+  ]
+}

.vscode/launch.json

@@ -0,0 +1,30 @@
+{
+  "version": "0.2.0",
+  "configurations": [
+    {
+      "name": "Flask API (:5001)",
+      "type": "debugpy",
+      "request": "launch",
+      "module": "flask",
+      "cwd": "${workspaceFolder}",
+      "env": {
+        "FLASK_APP": "shopdb",
+        "FLASK_ENV": "development",
+        "FLASK_DEBUG": "1"
+      },
+      "args": ["run", "--port", "5001", "--no-reload"],
+      "jinja": true,
+      "justMyCode": false,
+      "console": "integratedTerminal"
+    },
+    {
+      "name": "Pytest (current file)",
+      "type": "debugpy",
+      "request": "launch",
+      "module": "pytest",
+      "cwd": "${workspaceFolder}",
+      "args": ["${file}", "-v"],
+      "console": "integratedTerminal"
+    }
+  ]
+}

.vscode/tasks.json

@@ -0,0 +1,43 @@
+{
+  "version": "2.0.0",
+  "tasks": [
+    {
+      "label": "Backend: flask run (:5001)",
+      "type": "shell",
+      "command": "${workspaceFolder}/venv/bin/flask run --port 5001",
+      "options": {
+        "cwd": "${workspaceFolder}",
+        "env": { "FLASK_APP": "shopdb" }
+      },
+      "windows": {
+        "command": "${workspaceFolder}\\venv\\Scripts\\flask.exe run --port 5001"
+      },
+      "isBackground": true,
+      "problemMatcher": []
+    },
+    {
+      "label": "Frontend: npm run dev (:5173)",
+      "type": "shell",
+      "command": "npm run dev",
+      "options": { "cwd": "${workspaceFolder}/frontend" },
+      "isBackground": true,
+      "problemMatcher": []
+    },
+    {
+      "label": "Dev site (backend + frontend)",
+      "dependsOn": [
+        "Backend: flask run (:5001)",
+        "Frontend: npm run dev (:5173)"
+      ],
+      "dependsOrder": "parallel",
+      "problemMatcher": []
+    },
+    {
+      "label": "Check: naming + tests + build",
+      "type": "shell",
+      "command": "bash scripts/check-naming-and-style.sh && venv/bin/python -m pytest tests/ -q && cd frontend && npx vitest run && npm run build",
+      "options": { "cwd": "${workspaceFolder}" },
+      "problemMatcher": []
+    }
+  ]
+}