add-theme

# add-theme 1. Read the `Theme` struct in `crates/pixtuoid-scene/src/theme/mod.rs` and an existing theme (e.g. `theme/dracula.rs`) for the full field set. 2. Create `crates/pixtuoid-scene/src/theme/<name>.rs` defining `pub static <NAME>: Theme = Theme { ... }`. 3. Register it: add the `mod` in `theme/mod.rs` and append `&<NAME>` to the `ALL_THEMES` slice; its `name` field is the kebab-case `--theme` id. 4. Add a row to `site/src/themes.json` (`id` = the kebab-case `name`, plus its presentation fields). `theme_gallery_manifest_matches_all_themes` asserts the manifest ids == `ALL_THEMES` names — the site never runs the binary, so this bridge test is the only guard that its theme switcher stays in sync. Then run `just gen-media` to regenerate the committed theme stills (else the smoke `gen-check` reds the PR). 5. Theme roles **may share an RGB** (every bundled theme does). What binds you are the `*_for_every_theme` legibility guards in `theme/mod.rs`. 6. Run `just test`; update insta snapshots if the theme list changed. 7. Visually verify with the **beautify-decoration** skill's snapshot loop — a palette that passes the legibility guards can still read badly. 8. `just preflight full`, then the **two-lens-review** skill — the regenerated stills fire REVIEW.md's local "Generated art / clips" row.