Add a real background image to the ending screen

Same treatment as the intro: generated desk photo (empty chair, a
single closed box where the stamp used to be, one dark pigeonhole
slot) converted PNG -> WebP, 1.7MB -> 45KB. Used for both win and
loss endings, since the image itself is mood-neutral rather than
victory- or failure-specific — the audit-stamp overlay (TILLSVIDARE
in green, OMPLACERAD/AVFÖRD in red) still carries the actual outcome.

.end-card switched from an opaque panel to a translucent one with a
backdrop blur so the photo is actually visible around and through the
card instead of fully hidden behind it — same fix .seal already
needed on the intro screen.

Verified by injecting all three real end states (clean win,
composure-driven loss, suspicion-maxed loss) and screenshotting each.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

.gitignore

@@ -3,6 +3,7 @@ dist
 .env
 *.local
 
-# Raw source image — public/intro.webp is the optimized derivative that
-# actually ships; no need to bloat the repo with the 1.7MB original.
+# Raw source images — public/*.webp are the optimized derivatives that
+# actually ship; no need to bloat the repo with the 1.7MB originals.
 /intro.png
+/gameover.png