agent: move "sketch-base" into git

The agent's notion of "initial commit" is kind of special, in that it
is used as the "base" for a bunch of git operations. It's hard for
the user to change (we only provide a workflow via restart), yet
sometimes you want to do just that.

So, instead we put it as data inside of it, named as a tag sketch-base.
It's abusing tags, but branches are no better.
diff --git a/.vscode/launch.json b/.vscode/launch.json
index d273789..9cd3e58 100644
--- a/.vscode/launch.json
+++ b/.vscode/launch.json
@@ -5,6 +5,16 @@
   "version": "0.2.0",
   "configurations": [
     {
+      "name": "debug go run sketch -unsafe",
+      "type": "go",
+      "request": "launch",
+      "mode": "debug",
+      "program": "${workspaceFolder}/cmd/sketch",
+      "args": ["-unsafe", "-verbose"],
+      "cwd": "${workspaceFolder}",
+      "console": "integratedTerminal"
+    },
+    {
       "type": "chrome",
       "request": "launch",
       "name": "Launch Chrome against localhost",