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>

.gitignore

@@ -38,10 +38,21 @@ todo.md
 plans/
 .pi/hf-sessions/
 .pi/hf-sessions-backup/
-.pi/agent/
 .pi/sessions/
 .pi/extensions/webui/.webui.pid
 .pi/extensions/webui/.webui.log
+# Pi agent: track extensions, ignore local runtime secrets and sessions
+.pi/agent/sessions/
+.pi/agent/git/
+.pi/agent/npm/
+.pi/agent/auth.json
+.pi/agent/models.json
+.pi/agent/settings.json
+.pi/agent/mcp-cache.json
+.pi/agent/run-history.jsonl
+.pi/agent/extensions/webui/frontend/node_modules/
+.pi/agent/extensions/webui/.webui.pid
+.pi/agent/extensions/webui/data/
 tmp/
 bun.lock
 collect.sh