app icon: unicorn (owner's ArtCraft drawing), Dock/taskbar/launcher wiring, palette docs

- assets/app-icon/: master and light SVGs, 1024 px PNG, .icns (Apple grid), .ico (16-256),
  hicolor 16-512 + scalable, LICENSE.txt, README with palette (#e0368f / #efe9dc / #0b0b0c),
  tile geometry and provenance; attribution sidecars + ATTRIBUTION.md rows.
- packaging/icons.sh regenerates everything with resvg, iconutil and the new `cargo xtask ico`.
- Runtime icon via ViewportBuilder::with_icon (padded variant on macOS) and Wayland app ID
  ai.storyteller.effectcraft; packaging/linux/ai.storyteller.effectcraft.desktop.
- apps/effectcraft/build.rs embeds the .ico and VERSIONINFO into effectcraft.exe (winresource,
  Windows targets only; a missing resource compiler is a warning).
- Web favicon.svg is now the unicorn icon.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

packaging/linux/ai.storyteller.effectcraft.desktop

@@ -0,0 +1,13 @@
+[Desktop Entry]
+Type=Application
+Name=EffectCraft
+GenericName=Motion Graphics Editor
+Comment=Motion graphics and visual effects compositor
+Exec=effectcraft %F
+TryExec=effectcraft
+Icon=ai.storyteller.effectcraft
+Terminal=false
+StartupNotify=true
+StartupWMClass=ai.storyteller.effectcraft
+Categories=AudioVideo;Video;Graphics;2DGraphics;
+Keywords=motion;graphics;animation;compositor;effects;keyframe;vfx;