[ch0rizo]

Description

Fixes receipts that show "sendt på mail" but never reach the økans or the submitter.

Since the move to fpdf2 (#1529), HDR phone JPEGs, which Pillow reads as MPO, are embedded as raw pixels. Three ~3.5 MB photos made a ~90 MB email, far over Gmail's 25 MB limit. Gmail accepted it and then dropped it, so nobody got anything.

• Uploads are straightened (EXIF), downscaled to max 2400 px and re-encoded as JPEG. 3 HDR photos: 91 MB → 3 MB. Sideways portrait photos are fixed too.
• If the PDF is still over 25 MB, the user gets a clear error instead of a false success.
• The form keeps its values on errors, so the user can remove attachments and resubmit.
• Network errors now show a message instead of failing silently.

Result

If you've made visual changes, please check the boxes below and include images showing the changes. Descriptions are appreciated.

• Changes look good with different viewports (mobile, tablet, etc.).
• Changes look good with slower Internet connections.

Testing

• I have thoroughly tested my changes.

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Resolves #1533