gui: Give home actions distinct artwork

[BenWestgate]

Tails 7.13 tester feedback: several home actions looked as though they used the same icon, making the six choices harder to distinguish at a glance.

Source inspection shows the six actions already reference six distinct bundled Codex32-book graphics. That means the report cannot safely be converted into an asset-replacement PR from filenames/source alone; the ambiguity may come from how two different graphics render at the supported guest resolution.

Required next step: during the final Tails visual pass for #74/#75, record which rendered home actions the tester actually confuses. Then make a small presentation-only asset/layout change if the rendered evidence still reproduces the problem. Keep the existing book style and bundled assets where possible; add no new icon dependency and change no workflow/wallet behavior.

This issue is intentionally deferred pending that human visual evidence. Do not guess an artwork replacement before the Tails pass, and do not treat it as resolved merely because the source filenames differ.

[BenWestgate]

Release-gate triage: the current clean GUI already maps the six home actions to six different bundled Codex32-book assets (sun, lock, potion, dragon, codex, bitcoin), and those files are distinct repository blobs. The tester's finding is therefore visual distinguishability at the rendered Tails size, not accidental asset reuse. I am not going to guess a replacement mapping from source names alone. Keep this gate item open for the next Tails visual pass; record which actions/graphics are being confused, then make the smallest asset/mapping adjustment from the existing book artwork and verify it in the same environment. This is explicitly deferred from #77 rather than silently treated as fixed.