Update the copyright holder and year

[sandhose]

This can be reviewed commit by commit.

• Update screenshots with the current copyright year
• Merge the annotations in REUSE.toml into a single one
• Update the copyright holder to Element Creations Ltd.

Most of the heavy lifting was done using:

uvx reuse annotate \
  -y 2026 \
  --merge-copyrights \
  -c 'Element Creations Ltd.' \
  -l 'AGPL-3.0-only OR LicenseRef-Element-Commercial' \
  --copyright-prefix spdx-string \
  $(git ls-files)