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.md

@@ -54,7 +54,7 @@ Start here, don't re-derive from scratch:
   live (mobile viewport CSS collapse, a dialog's status message landing
   behind its own backdrop, a JSON/form-urlencoded body mismatch). Spin up
   `uvicorn app.main:app` against a scratch `DATABASE_URL`/`CONFIG_PATH`
-  sqlite file, don't touch the real deployment's data. `server/.claude/skills/run-server/`
+  sqlite file, don't touch the real deployment's data. `.claude/skills/run-server/`
   (`/run-server`) has a driver for exactly this.
 - **New/changed UI must work at both desktop and mobile widths --
   screenshot both, don't assume one implies the other.** The layout