Fix Garmin connect race, surface tool error content, add dev start scripts

- GarminConnection now flushes Profile's pending debounced autosave before
  connecting, avoiding a race where Connect fires with stale credentials.
- client.go reads res.Content before checking IsError so tool error
  messages actually include mcp-garmin's response text.
- seedsample: update kind lookups to match current taxonomy names
  ("Easy Run" -> "Easy", "Interval" -> "Intervals").
- Add backend/start.sh and frontend/start.sh dev launch scripts, and
  check in CLAUDE.md.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

backend/start.sh

@@ -0,0 +1,9 @@
+#!/usr/bin/env bash
+set -euo pipefail
+cd "$(dirname "$0")"
+
+export MCP_GARMIN_PYTHON="${MCP_GARMIN_PYTHON:-/Users/cvila/Dev/scm/scm.vilanet.fr/kriss/mcp-garmin/.venv/bin/python3}"
+export MCP_GARMIN_SERVER="${MCP_GARMIN_SERVER:-/Users/cvila/Dev/scm/scm.vilanet.fr/kriss/mcp-garmin/server.py}"
+export SMARTRUN_DB_PATH="${SMARTRUN_DB_PATH:-smartrun.db}"
+
+exec go run ./cmd/smartrund