Give the menu entry our own logo

The entry borrowed the Ports icon, because that was the only way for a
custom ES system to have any artwork at all: EmulationStation resolves a
system's carousel logo through the theme, and there is no user-level
override. Engine 4.2 installs a logo into the themes instead, so this store
ships one — the TTG mark from media/TTG-Logo.png, keyed out of its
background and cropped, plus a vector "TTG" for the themes that only look
for an SVG.

The theme folder now defaults to the store id rather than `ports`, so the
file is ours and no theme's own artwork is overwritten.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

config.json

@@ -17,8 +17,11 @@
   "emulationstation": {
     "menu": {
       "mode": "system",
-      "theme": "ports",
-      "updater": true
+      "updater": true,
+      "logo": [
+        "https://git.teletypegames.org/stores/ttg-batocera-store/raw/branch/master/logo.png",
+        "https://git.teletypegames.org/stores/ttg-batocera-store/raw/branch/master/logo.svg"
+      ]
     },
     "restart": true
   },