[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/src/api/assets.rs

@@ -367,14 +367,22 @@ mod tests {
             ("aprs-symbols-24-1", status::APRS_SYMBOLS_ALTERNATE),
             ("aprs-symbols-24-2", status::APRS_SYMBOLS_OVERLAY),
         ] {
-            assert_eq!(png_dimensions(bytes), (384, 144), "{name} is not a 16x6 grid");
+            assert_eq!(
+                png_dimensions(bytes),
+                (384, 144),
+                "{name} is not a 16x6 grid"
+            );
         }
         for (name, bytes) in [
             ("aprs-symbols-24-0-2x", status::APRS_SYMBOLS_PRIMARY_2X),
             ("aprs-symbols-24-1-2x", status::APRS_SYMBOLS_ALTERNATE_2X),
             ("aprs-symbols-24-2-2x", status::APRS_SYMBOLS_OVERLAY_2X),
         ] {
-            assert_eq!(png_dimensions(bytes), (768, 288), "{name} is not a 2x sheet");
+            assert_eq!(
+                png_dimensions(bytes),
+                (768, 288),
+                "{name} is not a 2x sheet"
+            );
         }
     }
 }

src/trx-client/trx-frontend/trx-frontend-http/src/status.rs

@@ -41,7 +41,8 @@ pub const LEAFLET_LAYERS_2X: &[u8] = include_bytes!("../assets/web/vendor/layers
 // Each sheet is a 16x6 grid of 24px cells indexed by `symbol code - 0x21`:
 // table 0 is the primary ('/') set, table 1 the alternate ('\') set, and
 // table 2 the overlay characters drawn on top of an alternate symbol.
-pub const APRS_SYMBOLS_PRIMARY: &[u8] = include_bytes!("../assets/web/vendor/aprs-symbols-24-0.png");
+pub const APRS_SYMBOLS_PRIMARY: &[u8] =
+    include_bytes!("../assets/web/vendor/aprs-symbols-24-0.png");
 pub const APRS_SYMBOLS_PRIMARY_2X: &[u8] =
     include_bytes!("../assets/web/vendor/aprs-symbols-24-0-2x.png");
 pub const APRS_SYMBOLS_ALTERNATE: &[u8] =