refactor(store): single account name on users; rename profile/laps tables

users.display_name becomes users.name and is now the only human-facing
name -- profiles.name is dropped (it duplicated the account name; the
Profile page's Name field now edits users.name through PUT /api/profile,
which carries Name alongside the profiles columns). The profile table
becomes profiles and laps becomes activity_laps, homogeneous with
activity_samples. Onboarding pre-fills the display name from the OIDC
claim's name.

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

backend/internal/api/server.go

@@ -184,7 +184,7 @@ func loggingMiddleware(next http.Handler) http.Handler {
 		if ww.Status() >= 500 {
 			level = slog.LevelWarn
 		}
-		logger.LogAttrs(r.Context(), level, "http request",
+		logger.LogAttrs(r.Context(), level, "HTTP request",
 			slog.String("method", r.Method),
 			slog.String("path", r.URL.Path),
 			slog.Int("status", ww.Status()),