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/internal/garmin/client.go

@@ -146,15 +146,15 @@ func (c *mcpClient) callTool(ctx context.Context, name string, args map[string]a
 	if err != nil {
 		return "", fmt.Errorf("call tool %s: %w", name, err)
 	}
-	if res.IsError {
-		return "", fmt.Errorf("tool %s returned an error result", name)
-	}
 	var out strings.Builder
 	for _, content := range res.Content {
 		if tc, ok := content.(mcp.TextContent); ok {
 			out.WriteString(tc.Text)
 		}
 	}
+	if res.IsError {
+		return "", fmt.Errorf("tool %s returned an error result: %s", name, out.String())
+	}
 	return out.String(), nil
 }