feat(theme): add vscode-modern and vscode-2026 themes

[brycewc]

Summary

Adds two new VS Code themes, both following the same single-paired-theme pattern as the existing vscode theme (light mode uses the light palette, dark mode uses the dark palette):

• vscode-modern — matches VS Code's official Dark Modern and Light Modern themes (the current VS Code defaults).
• vscode-2026 — a newer VS Code default palette.

Colors

Base text comes from each theme's editor.foreground; token colors are the syntax colors those themes inherit.

vscode-modern

Token	Light	Dark
base text	#3b3b3b	#cccccc
property (key)	#0451a5	#9cdcfe
number / index	#098658	#b5cea8
string	#a31515	#ce9178
boolean / null	#0000ff	#569cd6

vscode-2026

Token	Light	Dark
base text	#1f2328	#c9d1d9
property (key)	#116329	#7ee787
number / index	#0550ae	#79c0ff
string	#0a3069	#a5d6ff
boolean / null	#0550ae	#79c0ff

Changes

• src/style.css / src/dark.css — light and dark palettes for .json-view_vscode-modern and .json-view_vscode-2026
• src/components/json-view.tsx — added 'vscode-modern' and 'vscode-2026' to the theme union
• src/stories/share.ts — Storybook control options
• src/stories/theme.stories.tsx — Vscode_Modern / Vscode_Modern_Dark and Vscode_2026 / Vscode_2026_Dark stories
• website/src/contents/themes.tsx — theme list + preview background colors
• README.md — documented the new options

Each new theme is placed directly after vscode in every list (vscode → vscode-modern → vscode-2026).

[vercel]

@brycewc is attempting to deploy a commit to the Suni's projects Team on Vercel.

A member of the Team first needs to authorize it.

[brycewc]

Superseded by #79 — the branch was renamed to new-vscode-themes (which auto-closed this PR since GitHub can't re-point a cross-fork PR on rename). Continuing there.