feat(stylebook): add Vue Styleguidist browser-based component stylebook and inline component docs

[remko48]

Summary

Closes #120

This PR introduces a fully functional browser-based stylebook for the component library using Vue Styleguidist, and adds inline .md documentation to every component directory. It also resolves Vue prop-validation console errors across all component categories that were surfaced by running the styleguide.

What changed

Styleguide setup (styleguide/)

• Added styleguide.config.js with full Vue Styleguidist configuration including aliases, webpack overrides, and global style injection
• Added setup.js to register Nextcloud globals, Pinia, Vue Router, and translation stubs before each example renders
• Added mocks for @nextcloud/l10n, @nextcloud/l10n-gettext, and empty module stubs so examples run without a real Nextcloud backend
• Added nextcloud-globals.css and nextcloud-tokens.css to simulate Nextcloud's design-token environment inside the styleguide
• Added nextcloud-tokens.md — a standalone design-token reference page in the styleguide
• Added favicon and custom theme CSS

Inline component documentation

• Added ComponentName.md files to every component directory (covers all ~50 components)
• Each file contains a description, prop/event/slot reference table, and at least one live code example
• Updated check-docs.js to verify coverage for both docs/components/*.md and src/components/*/*.md so CI catches gaps in either location

Console error fixes

• Fixed Vue prop-type validation warnings across all component categories: Data Display, Cards, Dialogs, Object Widgets, Dashboard, Full pages, App Shell, Settings, and Specialized components
• Corrected prop defaults, type declarations, and removed invalid attribute bindings that caused hydration warnings

Styling fixes

• Fixed table row hover state
• Fixed button sizing/alignment
• Fixed sidebar styling
• Fixed <main> tag styling
• Ensured only selected items are shown in the context menu

Documentation and CI

• Added GitHub Actions workflows for publishing the styleguide on development and beta branches (alongside the existing main workflow)
• Updated documentation.yml to integrate the styleguide build step

Test plan

• Run cd styleguide && npm install && npm run styleguide and confirm the styleguide opens in the browser with all components listed
• Verify no console errors appear in the browser when browsing component examples
• Run npm run check:docs from the repo root and confirm it exits 0
• Run npm test and confirm all existing tests pass
• Open a few component pages (e.g. CnDataTable, CnIndexPage, CnFormDialog) and verify the live examples render correctly

[SudoThijn]

looks fine to me.

[SudoThijn]

I did find one thing that can be fixed

Suggested change

	exclude: /node_modules\/(?!(@nextcloud|unified|vfile|lowlight|mdast-util|hast-util|unist-util|remark|rehype|micromark|decode-named-character-reference|bail|is-plain-obj|trim|trough|vfile-message|property-information))/,
	exclude: /node_modules\/(?!(@nextcloud|unified|vfile|lowlight|mdast-util|hast-util|unist-util|remark|rehype|micromark|decode-named-character-reference|bail|is-plain-obj|trim|trough|vfile-message|property-information|vue-codemirror6|codemirror|@codemirror|@lezer|gridstack|axios))/,

[SudoThijn]

I thought I found it all.

Under AppShell there is this weird white box

Highlighted for easier viewing