fix: eradicate tailwind @apply usage in vue styles (#9146)

## Summary

Remove Tailwind `@apply` from Vue styles across `src/` and
`apps/desktop-ui/src/` to align with Tailwind v4 guidance, replacing
usages with template utilities or native CSS while preserving behavior.

## Changes

- **What**:
- Batch 1: migrated low-risk template/style utility bundles out of
`@apply`.
- Batch 2: converted PrimeVue/`:deep()` override `@apply` blocks to
native CSS declarations.
- Batch 3: converted `src/components/node/NodeHelpContent.vue` markdown
styling from `@apply` to native CSS/token-based declarations.
- Batch 4: converted final desktop pseudo-element `@apply` styles and
removed stale `@reference` directives no longer required.
- Verified `rg -n "^\s*@apply\b" src apps -g "*.vue"` has no real CSS
`@apply` directives remaining (only known template false-positive event
binding in `NodeSearchContent.vue`).

## Review Focus

- Visual parity in components that previously depended on `@apply` in
`:deep()` selectors and markdown content:
  - topbar tabs/popovers, dialogs, breadcrumb, terminal overrides
  - desktop install/dialog/update/maintenance surfaces
  - node help markdown rendering
- Confirm no regressions from removal of now-unneeded `@reference`
directives.

## Screenshots (if applicable)

- No new screenshots included in this PR.
- Screenshot Playwright suite was run with `--grep="@screenshot"` and
reports baseline diffs in this environment (164 passed, 39 failed, 3
skipped) plus a teardown `EPERM` restore error on local path
`C:\Users\DrJKL\ComfyUI\LTXV\user`.

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-9146-fix-eradicate-tailwind-apply-usage-in-vue-styles-3116d73d3650813d8642e0bada13df32)
by [Unito](https://www.unito.io)

---------

Co-authored-by: Amp <amp@ampcode.com>
Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>

browser_tests/fixtures/selectors.ts

@@ -44,6 +44,12 @@ export const TestIds = {
   node: {
     titleInput: 'node-title-input'
   },
+  selectionToolbox: {
+    colorPickerButton: 'color-picker-button',
+    colorPickerCurrentColor: 'color-picker-current-color',
+    colorBlue: 'blue',
+    colorRed: 'red'
+  },
   widgets: {
     decrement: 'decrement',
     increment: 'increment',
@@ -74,6 +80,7 @@ export type TestIdValue =
   | (typeof TestIds.nodeLibrary)[keyof typeof TestIds.nodeLibrary]
   | (typeof TestIds.propertiesPanel)[keyof typeof TestIds.propertiesPanel]
   | (typeof TestIds.node)[keyof typeof TestIds.node]
+  | (typeof TestIds.selectionToolbox)[keyof typeof TestIds.selectionToolbox]
   | (typeof TestIds.widgets)[keyof typeof TestIds.widgets]
   | (typeof TestIds.breadcrumb)[keyof typeof TestIds.breadcrumb]
   | Exclude<