Upgrade Vite stack and simplify config

Vite config simplification

Replaced verbose per-option plugin config with frontendRoute:

// before
frappeui({
  frappeProxy: true,
  lucideIcons: true,
  jinjaBootData: true,
  buildConfig: { indexHtmlPath: '../gameplan/www/g.html' },
})

// after
frappeui({
  frontendRoute: '/g',
})

frappe-ui now derives proxy, build output path, and __FRONTEND_ROUTE__ compile-time constant from the single frontendRoute option. The router uses __FRONTEND_ROUTE__ instead of the hardcoded /g/ base path.

Remove tiptap resolve plugin

createResolveTiptapPlugin is no longer needed — frappe-ui and gameplan now use the same tiptap v3 version, so there are no conflicting resolutions to fix.

Dependency upgrades

• Vite 4 → 8
• @vitejs/plugin-vue 4 → 6
• @vitejs/plugin-vue-jsx 3 → 5
• @tiptap/* 2 → 3
• frappe-ui 0.1.261 → 0.1.269

Switch from pnpm to yarn

pnpm's strict dependency isolation prevents Vite 8 from discovering transitive CJS dependencies (like highlight.js and interactjs) for pre-bundling. Switched to yarn which hoists dependencies flat, matching frappe-ui's own package manager.

Updated all references: root scripts, CI workflow, devcontainer setup, and README.