Fix image expectations: README language & user docs

[ggfevans]

Summary

Issue #1517 revealed that the README promises "real device images so it actually looks like your gear, not sad grey boxes" but only 28% of devices (179/634) have bundled product images. Users expect photos by default but see coloured label blocks.

Deliverables

• Fix README language — replace misleading "real device images" line with accurate description
• Create user-facing image system docs covering:
  • Which brands have bundled images and approximate coverage
  • How to use display mode toggle (I key cycles label → image → image-label)
  • How to upload custom images (select device → EditPanel → Choose File)
  • Starter library: 11 generic devices all include images out of the box
  • Custom device types: no bundled images, but upload works the same way
• Reply to Pictures of assets #1517 with guidance and link to new docs

Success Criteria

Reporter's question is answered. New users landing on README have accurate expectations about image availability.

Related

• Pictures of assets #1517 — original report
• Part of: Device Image System improvements (Phase 1)

Design Spec

docs/superpowers/specs/2026-03-27-device-image-system-design.md