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/iron_ingot.svg

@@ -0,0 +1,8 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 100 100" width="100" height="100">
+  <g stroke="#2f343b" stroke-width="3.5" stroke-linejoin="round">
+    <path d="M28 72 L72 72 L64 54 L36 54 Z" fill="#a2a9b0"/>
+    <path d="M64 54 L72 72 L82 64 L74 46 Z" fill="#868d95"/>
+    <path d="M36 54 L64 54 L74 46 L46 46 Z" fill="#c8ced4"/>
+  </g>
+  <path d="M40 63 L60 63" stroke="#c2c7cd" stroke-width="3" stroke-linecap="round"/>
+</svg>