[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/frontend/tests/bundle-entry.mjs

@@ -4,7 +4,7 @@
 
 import { build } from "esbuild";
 
-export async function bundleEntry(entryUrl) {
+export async function bundleEntry(entryUrl, globalName) {
   const result = await build({
     entryPoints: [entryUrl.pathname],
     bundle: true,
@@ -12,6 +12,7 @@ export async function bundleEntry(entryUrl) {
     platform: "browser",
     target: "es2022",
     write: false,
+    ...(globalName ? { globalName } : {}),
   });
   const output = result.outputFiles[0];
   if (!output) throw new Error(`No bundle output for ${entryUrl.pathname}`);