feat(seoul256): add Seoul256 along hard and soft variants

[VuiMuich]

Description

Initial inspiration came frome the builtin seoul256 themes in the helix editor.
From there some research about the theme origin lead me throught the vim theme to it supposed origin. This last url was handed to claude to create a basic set of themes which later where manually refined.
I put some extra effort in fine tuning the terminal colors, since this feels for me like an important and sadly often overlookd part of a theme.

The hard and soft variants differ mostly in harder or softer surface shades and some minor contrast adjustments.
I have been daily driving this theme the last couple of weeks refining it to the current state.

(If you want me to explicitly split the themes into separate PRs, or want to reject the variants, let me know, I am happy to split or adjust the PR.)

PS: I adjusted onPrimary to produce a contrast of 3.0:1 and fixed an issue I overlooked with the cyan value

Screenshots

Please attach screenshots of your palette applied in Noctalia for both themes:

Dark theme

Seoul 256

Seoul256 Hard

Seoul256 Soft

Light theme

Seoul 256

Seoul256 Hard

Seoul256 Soft

Checklist

• I have tested my palette in Noctalia with the dark theme
• I have tested my palette in Noctalia with the light theme
• Screenshots for both themes are attached above

[github-actions]

Automatic Palette Check

---

File: Seoul256 Hard/Seoul256 Hard.json

• Low contrast mOnPrimary on mPrimary in light: 2.51:1 (#dadada on #a9824b), under 3.0:1

---

File: Seoul256 Soft/Seoul256 Soft.json

• Low contrast mOnPrimary on mPrimary in light: 2.51:1 (#dadada on #a9824b), under 3.0:1

---

File: Seoul256/Seoul256.json

• Low contrast mOnPrimary on mPrimary in light: 2.51:1 (#dadada on #a9824b), under 3.0:1

---

Low-contrast pairs are a warning, not a rejection: they do not fail this check.

[VuiMuich]

The CI report is outdated with the latest force-push, no warnings reported any more on a local run:

✦ >>> .github/workflows/contrast-check.sh | grep Seoul
noctalia-community-palettes on  seoul256 via ❄️  impure took 10s 

[VuiMuich]

🎉 thanks for the merge!