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 <[email protected]>

README.md

@@ -7,6 +7,10 @@
   </a>
 </p>
 
+<p align="center">
+  <img alt="EffectCraft app icon: an engraved unicorn on EffectCraft pink (#e0368f)" src="assets/app-icon/effectcraft-1024.png" width="128">
+</p>
+
 <h1 align="center">EffectCraft</h1>
 
 <p align="center">