feat(colors): add Neovim wallpaper theming and update failure surfacing

[yukazakiri]

Summary

Add wallpaper-driven Neovim/LazyVim theming through the existing color module pipeline, with a static generated spec that live-reloads from generated palette inputs instead of rewriting the plugin config on every wallpaper switch.

Also improve shell update failure handling by persisting update status/log paths and surfacing failures in the update overlay instead of silently clearing state.

compressO-recording_2026-04-01_16.22.15.mp4

Testing

• inir restart && inir logs — no errors
• Tested the specific feature path that changed
• Both panel families checked (if shared code changed)

Notes

• Verified the Neovim live-reload path in headless Neovim by atomically replacing palette.json and confirming the running session reloaded the theme.
• Shell update overlay/status changes were not exercised end to end in this branch.

Closes #