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>

scripts/new-feature.sh

@@ -0,0 +1,21 @@
+#!/usr/bin/env bash
+# Create a feature branch from latest main.
+set -euo pipefail
+
+if [[ $# -lt 1 ]]; then
+	echo "Usage: $0 <feature-name>" >&2
+	echo "Example: $0 webui-avatar-fix" >&2
+	exit 1
+fi
+
+ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
+cd "$ROOT"
+
+NAME="$1"
+BRANCH="feature/$NAME"
+
+git checkout main
+git pull --ff-only origin main 2>/dev/null || true
+git checkout -b "$BRANCH"
+
+echo "Created and switched to $BRANCH"