fix(contacts): adversarial-review fixes — delete UB, JPEG decode, footer clip

From an adversarial review of the avatar edit-dialog + image picker:

- HIGH: the per-row Delete icon called doDelete() (which erases from
  book.entries()) INSIDE the loop iterating that same vector — out-of-bounds
  reads / wrong rows on the confirming click. Defer it until after the loop.
- HIGH: the decode stack was compiled PNG-only (STBI_ONLY_PNG) while the image
  picker accepts .jpg/.jpeg/.bmp/.gif, so picking a JPEG (the common photo
  case) silently produced a non-loading avatar + an orphaned copy on disk.
  Enable JPEG/BMP/GIF decoders, and guard the pick: verify the source decodes
  before copying/committing (new contact_avatar_bad_image string, 8 langs).
- MED: the fixed, non-scrolling edit card floored bodyH at 260*dp, which could
  push Save/Cancel below the card on short windows — floor lowered so the
  footer always stays inside.
- LOW: the live-preview panel rounding is now dp-scaled (10*dp) to match the
  real list card it mirrors.
- LOW: re-picking the same source path after its contents changed showed a
  stale cached texture — evict the avatar texture cache entry on re-pick.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

res/lang/de.json

@@ -288,6 +288,7 @@
     "console_zoom_in": "Vergrößern",
     "console_zoom_out": "Verkleinern",
     "contact_avatar": "AVATAR",
+    "contact_avatar_bad_image": "Dieses Bild konnte nicht geladen werden.",
     "contact_avatar_badge": "Abzeichen",
     "contact_avatar_badge_hint": "Das Abzeichen wird automatisch anhand des Adresstyps gewählt.",
     "contact_avatar_choose": "Bild auswählen…",