Upgrade Flutter 3.44.2, iOS→SPM, logging, icons, publishing CI

[Medformatik]

Accumulated upgrade + publishing work. Each item is a separate commit.

Changes

• Flutter 3.44.2 + dependency upgrades (incl. flutter_local_notifications 22, logging); kept the required uuid override.
• Linux: migrated to the modern linux/runner/ layout (custom code preserved).
• iOS: migrated CocoaPods → Swift Package Manager (all iOS plugins now support SPM); macOS stays hybrid (system_tray has no SPM yet).
• Logging: replaced ~200 print() calls with package:logging (named loggers, levels) and re-enabled the avoid_print lint.
• macOS: tray icon now rendered as a template image (adapts to light/dark menu bar).
• Icons: new app + tray icons; regenerated iOS/macOS sets via flutter_launcher_icons; removed unused .ico leftovers.
• CI/release: single ci.yml (format/analyze/test once → per-platform builds) and tag-triggered release.yml (signed+notarized macOS, Linux AppImage+tarball, Homebrew cask); added Dependabot.

Verification

• flutter analyze clean, flutter test 10/10.
• flutter build macos --release, flutter build ios --simulator, iOS SPM build all verified locally.
• Linux build not verified locally (no GTK on macOS) — relies on CI.

Release signing requires Apple Developer secrets (not yet configured); see release.yml header.