Add item icon art for all 41 item types

Self-contained full-color SVGs in data/icons/items/, one per item id, read
by the recipe-selection dialog (REQ-UI-RECIPE-ICON) and belt/port rendering
(REQ-UI-ITEM-ICON). Bold silhouette + dark outline, authored to stay legible
at ~16px belt size: rocky ore chunks, isometric ingots, riveted plates,
copper coil/wire, pictorial module devices, and dart hull silhouettes tinted
per fleet color. No config changes needed — each recipe's icon resolves to
its first output.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Y7N59FsLA5e2kuVdqe4Uhc

bin/app/data/icons/items/silicon.svg

@@ -0,0 +1,6 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 100 100" width="100" height="100">
+  <circle cx="50" cy="52" r="33" fill="#33415e" stroke="#0e1420" stroke-width="3.5"/>
+  <line x1="35" y1="27" x2="52" y2="22" stroke="#0e1420" stroke-width="4" stroke-linecap="round"/>
+  <circle cx="50" cy="52" r="21" fill="none" stroke="#46567a" stroke-width="2.6"/>
+  <circle cx="42" cy="44" r="5" fill="#5d6f96"/>
+</svg>