Add a mobile visual check for the curated example

[p13i]

Gap

The curated example implements 900-pixel and 600-pixel
breakpoints, but its evidence states that no physical mobile
device was visually tested.

Acceptance criteria

• Capture the committed example at a documented mobile
  viewport.
• Check heading hierarchy, card order, horizontal overflow,
  table or timeline clipping, and source labels.
• Retain a reproducible screenshot command and evidence
  hash.
• Do not claim physical-device coverage if the run uses
  browser emulation.

Verification

Run make check and the documented mobile capture command.

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Written by Codex