Tighten item icon viewBoxes so art fills the slot

Each icon's viewBox is set to a square box around its actual content
(with a stroke-width margin + small breathing room), leaving the path
data unchanged. Under-filled icons (ingots, plates, silicon, etc.) now
scale up and recenter to fill the half-tile item slot; already-full
icons are left as-is (clamped to only ever zoom in). Fixes items looking
too small in the game world.

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

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

@@ -1,4 +1,4 @@
-<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 100 100" width="100" height="100">
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="15.8 15.8 68.4 68.4" width="100" height="100">
   <path d="M50 20 L76 35 L76 65 L50 80 L24 65 L24 35 Z" fill="#e0d8c8" stroke="#3a3428" stroke-width="3.5" stroke-linejoin="round"/>
   <path d="M50 32 L64 40 L64 60 L50 68 L36 60 L36 40 Z" fill="#efe9dd" stroke="#3a3428" stroke-width="2"/>
 </svg>