Move make-widget/run-server skills to root .claude/skills/

Nested .claude/skills/ dirs (previously under server/) are only
auto-discovered on-demand once a file under that subdirectory is
touched, so /make-widget and /run-server weren't invocable from a
fresh session. Root .claude/skills/ is scanned at session start.

Fixes setup.sh/start-server.sh's relative cd-depth math (was hardcoded
for the old server/.claude/skills/run-server/ depth) to instead
resolve the repo root via git and cd into server/ explicitly, and
updates SKILL.md/driver.py's path references to match the new layout.

.claude/skills/run-server/stop-server.sh

@@ -0,0 +1,10 @@
+#!/usr/bin/env bash
+# Usage: ./stop-server.sh [scratch-dir]
+SCRATCH="${1:-/tmp/run-server-scratch}"
+if [ -f "$SCRATCH/server.pid" ]; then
+  kill "$(cat "$SCRATCH/server.pid")" 2>/dev/null || true
+  rm -f "$SCRATCH/server.pid"
+  echo "stopped"
+else
+  echo "no $SCRATCH/server.pid -- nothing to stop"
+fi