ui(13e6): drop device-specific SSID chip placeholder

Replace the hardcoded "PictureFrame-91F8" in the AP setup screen with
a universal "PICTUREFRAME" brand chip. Firmware doesn't write text
into static .bin assets on this panel, so a per-device SSID placeholder
would lie on every other unit; the brand chip is the same image for
every frame.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

scripts/gen_screens_13e6.py

@@ -256,7 +256,10 @@ def gen_ap(accent=YL,
     img = Image.new("RGB", (W, H), WH)
     draw = ImageDraw.Draw(img)
 
-    draw_header(draw, accent, header_text, "PictureFrame-91F8")
+    # Universal brand chip — firmware doesn't write text into static .bin
+    # assets, so leaving a per-device SSID placeholder here would lie on
+    # every other unit. Same image for every frame.
+    draw_header(draw, accent, header_text, "PICTUREFRAME")
     draw_divider(draw)
 
     # ── LEFT COLUMN ──────────────────────────────────────────────────────────