Introduce lib/utils/log.dart (logError / logWarning over dart:developer) and
route all 53 previously-bare `catch (_)` blocks through it. Behaviour is
unchanged: every fallback still fails soft (a broken sidecar, unreadable file
or unsupported platform must never crash a presentation) but the cause is now
observable. logError is used for unexpected parse/IO failures, logWarning for
expected best-effort fallbacks; no deck or file contents are ever logged.
Note: file_service, markdown_service, marp_html_service, fullscreen_presenter,
image_carousel_picker and url_launcher_util also carried pre-existing local
changes, bundled here.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
