chore: configure project with src/ directory structure and tooling

- Move app files into src/ directory following Next.js convention
- Add baseUrl: src/ to tsconfig.json for path resolution
- Add .vscode/launch.json with debug configs for dev/build/start/lint
- Add lint:fix npm script to package.json

.vscode/launch.json

@@ -0,0 +1,50 @@
+{
+  "version": "0.2.0",
+  "configurations": [
+    {
+      "name": "Next.js: dev",
+      "type": "node",
+      "request": "launch",
+      "runtimeExecutable": "pnpm",
+      "runtimeArgs": ["run", "dev"],
+      "console": "integratedTerminal"
+    },
+    {
+      "name": "Next.js: build",
+      "type": "node",
+      "request": "launch",
+      "runtimeExecutable": "pnpm",
+      "runtimeArgs": ["run", "build"],
+      "console": "integratedTerminal"
+    },
+    {
+      "name": "Next.js: start",
+      "type": "node",
+      "request": "launch",
+      "runtimeExecutable": "pnpm",
+      "runtimeArgs": ["run", "start"],
+      "console": "integratedTerminal",
+      "serverReadyAction": {
+        "pattern": "- Local:.+(https?://.+)",
+        "uriFormat": "%s",
+        "action": "openExternally"
+      }
+    },
+    {
+      "name": "Next.js: lint",
+      "type": "node",
+      "request": "launch",
+      "runtimeExecutable": "pnpm",
+      "runtimeArgs": ["run", "lint"],
+      "console": "integratedTerminal"
+    },
+    {
+      "name": "Next.js: lint:fix",
+      "type": "node",
+      "request": "launch",
+      "runtimeExecutable": "pnpm",
+      "runtimeArgs": ["run", "lint:fix"],
+      "console": "integratedTerminal"
+    }
+  ]
+}