ux(ocr): full-bleed modal on mobile, buttons hug screen edges

@media (max-width: 640px):
- backdrop loses its 1 rem inset; modal goes 100vw × 100vh with
  no border-radius
- crop modal body keeps ~20 px horizontal padding so cropper
  corner handles stay safely outside Android's edge-swipe
  back-gesture zone (the corner DRAG is what triggers it; a tap
  on a button at the edge doesn't)
- camera viewfinder body has zero padding — video fills the
  whole space
- footer has minimal 0.5 rem padding so the rotate / invert /
  cancel / check buttons hug the screen edges
- iOS notch / home-indicator insets honoured via
  env(safe-area-inset-*)

Doesn't change the camera-confirm behaviour — that's the OS-camera
fallback path that fires when getUserMedia is denied for not being
a secure context (i.e. http://lan-ip:8000 from the phone, not
HTTPS or localhost).

CHANGELOG.md

@@ -25,6 +25,7 @@ Versioning: [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 ### Added
 - Camera viewfinder modal on mobile (via `navigator.mediaDevices.getUserMedia` with `facingMode: environment`) — replaces the `<input type=file capture>` flow. Tapping the shutter goes directly to the crop modal, skipping the OS-level "retake / use" confirm step. Falls back to the file picker if camera access is denied or unavailable; a "Pick from file" icon (`photo_library`) inside the camera modal also routes to the picker on demand.
 - Invert-colours toggle (`invert_colors`) in the crop modal. Tap to flip light-on-dark text into the dark-on-light polarity Tesseract expects. The grayscale buffer is inverted before adaptive thresholding so the binarised output is correct.
+- Mobile-first modal layout (≤ 640 px): the crop and camera modals now fill the viewport (no backdrop padding, no border-radius), buttons hug the screen edges in the footer, and the camera video occupies the entire body. Body still has ~20 px horizontal padding so cropper's corner handles stay outside Android's edge-swipe back-gesture zone. iOS notch / home-bar insets honoured.
 
 ### Fixed
 - "Hot: …" status no longer claims "unloads in X" when the server's `keep_alive` is `-1` (Ollama returns an absurd year-4001 `expires_at`). Threshold: any expiry >7 days drops the suffix and just shows the model name.