chore: add sproutclaw git workflow and track local extensions

Document main/upstream-sync/feature branch strategy, add sync/push
scripts, track .pi/agent extensions and webui in git, and disable
startup changelog via showChangelogOnStartup.

Co-authored-by: Cursor <cursoragent@cursor.com>

.pi/agent/settings.example.json

@@ -0,0 +1,14 @@
+{
+  "lastChangelogVersion": "0.75.4",
+  "showChangelogOnStartup": false,
+  "defaultProvider": "your-provider",
+  "defaultModel": "your-model",
+  "defaultThinkingLevel": "high",
+  "transport": "sse",
+  "theme": "dark",
+  "packages": [
+    "npm:pi-subagents",
+    "npm:pi-mcp-adapter",
+    "npm:pi-autocontext"
+  ]
+}