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/copper_coil.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="0.0 2.0 100.0 100.0" width="100" height="100">
   <circle cx="50" cy="52" r="42" fill="none" stroke="#3a1e08" stroke-width="2.5"/>
   <circle cx="50" cy="52" r="26" fill="none" stroke="#3a1e08" stroke-width="2.5"/>
   <circle cx="50" cy="52" r="34" fill="none" stroke="#cf7a2c" stroke-width="16"/>