[feat](trx-frontend-http): draw APRS symbols from the sprite sheets

Resolve a table/code pair to a sprite cell in aprs-shared, and use it
from both the packet lists and the map markers, which had each been
printing the raw symbol character in a bordered box.

A table identifier of / or \ selects the primary or alternate sheet
directly.  Anything else is an overlay character, which the APRS spec
draws on top of the alternate symbol -- so those stack the overlay sheet
over the alternate one rather than picking a sheet.  Codes outside
0x21..0x7E have no cell and keep the old character box.

The sheet URLs stay in the stylesheet so a min-resolution query can swap
in the retina sheets; only the cell offset is computed and set inline.
Map markers share the helper through the plugin chunk, so the map stays
free of any remote symbol fetch.

Verified in a browser against the real stylesheet and sheets: /> is a
car, /_ a WX circle, /& an igate diamond, \n a red triangle, and the
overlays S> and 7# carry their character on the alternate symbol.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018huL1ELyr86yVqfAabtioA
Signed-off-by: Stan Grams <sjg@haxx.space>

src/trx-client/trx-frontend/trx-frontend-http/assets/web/generated/aprs.js

@@ -7,7 +7,7 @@ import {
   normalizeAprsPacket,
   renderAprsInfo,
   renderLocalAprsSymbol
-} from "./chunk-M2I6DH4X.js";
+} from "./chunk-ROTCLFXS.js";
 import {
   hostCore,
   hostState