dev: add .vscode launch/tasks so F5 launches the extension host

Without launch.json, F5 in a fresh clone just prompts for a debug
environment. The 'Run Extension' configuration spawns an Extension
Development Host with this workspace loaded, with `npm: compile` as
a preLaunchTask so the extension always runs against an up-to-date
build.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.vscode/launch.json

@@ -0,0 +1,17 @@
+{
+  "version": "0.2.0",
+  "configurations": [
+    {
+      "name": "Run Extension",
+      "type": "extensionHost",
+      "request": "launch",
+      "args": [
+        "--extensionDevelopmentPath=${workspaceFolder}"
+      ],
+      "outFiles": [
+        "${workspaceFolder}/out/**/*.js"
+      ],
+      "preLaunchTask": "npm: compile"
+    }
+  ]
+}