Decouple Desktop UI into monorepo app (#5912)

## Summary

Extracts desktop UI into apps/desktop-ui package with minimal changes.

## Changes

- **What**:
- Separates desktop-specific code into standalone package with
independent Vite config, router, and i18n
- Drastically simplifies the main app router by removing all desktop
routes
  - Adds a some code duplication, most due to the existing design
- Some duplication can be refactored to be *simpler* on either side - no
need to split things by `isElectron()`
  - Rudimentary storybook support has been added
- **Breaking**: Stacked PR for publishing must be merged before this PR
makes it to stable core (but publishing _could_ be done manually)
  - #5915
- **Dependencies**: Takes full advantage of pnpm catalog. No additional
dependencies added.

## Review Focus

- Should be no changes to normal frontend operation
- Scripts added to root package.json are acceptable
- The duplication in this PR is copied as is, wherever possible. Any
corrections or fix-ups beyond the scope of simply migrating the
functionality as-is, can be addressed in later PRs. That said, if any
changes are made, it instantly becomes more difficult to separate the
duplicated code out into a shared utility.
  - Tracking issue to address concerns: #5925

### i18n

Fixing i18n is out of scope for this PR. It is a larger task that we
should consider carefully and implement properly. Attempting to isolate
the desktop i18n and duplicate the _current_ localisation scripts would
be wasted energy.

apps/desktop-ui/src/components/bottomPanel/tabs/terminal/BaseTerminal.vue

@@ -0,0 +1,113 @@
+<template>
+  <div
+    ref="rootEl"
+    class="relative overflow-hidden h-full w-full bg-neutral-900"
+  >
+    <div class="p-terminal rounded-none h-full w-full p-2">
+      <div ref="terminalEl" class="h-full terminal-host" />
+    </div>
+    <Button
+      v-tooltip.left="{
+        value: tooltipText,
+        showDelay: 300
+      }"
+      icon="pi pi-copy"
+      severity="secondary"
+      size="small"
+      :class="
+        cn('absolute top-2 right-8 transition-opacity', {
+          'opacity-0 pointer-events-none select-none': !isHovered
+        })
+      "
+      :aria-label="tooltipText"
+      @click="handleCopy"
+    />
+  </div>
+</template>
+
+<script setup lang="ts">
+import { useElementHover, useEventListener } from '@vueuse/core'
+import type { IDisposable } from '@xterm/xterm'
+import Button from 'primevue/button'
+import type { Ref } from 'vue'
+import { computed, onMounted, onUnmounted, ref } from 'vue'
+import { useI18n } from 'vue-i18n'
+
+import { useTerminal } from '@/composables/bottomPanelTabs/useTerminal'
+import { electronAPI, isElectron } from '@/utils/envUtil'
+import { cn } from '@/utils/tailwindUtil'
+
+const { t } = useI18n()
+
+const emit = defineEmits<{
+  created: [ReturnType<typeof useTerminal>, Ref<HTMLElement | undefined>]
+  unmounted: []
+}>()
+const terminalEl = ref<HTMLElement | undefined>()
+const rootEl = ref<HTMLElement | undefined>()
+const hasSelection = ref(false)
+
+const isHovered = useElementHover(rootEl)
+
+const terminalData = useTerminal(terminalEl)
+emit('created', terminalData, ref(rootEl))
+
+const { terminal } = terminalData
+let selectionDisposable: IDisposable | undefined
+
+const tooltipText = computed(() => {
+  return hasSelection.value
+    ? t('serverStart.copySelectionTooltip')
+    : t('serverStart.copyAllTooltip')
+})
+
+const handleCopy = async () => {
+  const existingSelection = terminal.getSelection()
+  const shouldSelectAll = !existingSelection
+  if (shouldSelectAll) terminal.selectAll()
+
+  const selectedText = shouldSelectAll
+    ? terminal.getSelection()
+    : existingSelection
+
+  if (selectedText) {
+    await navigator.clipboard.writeText(selectedText)
+
+    if (shouldSelectAll) {
+      terminal.clearSelection()
+    }
+  }
+}
+
+const showContextMenu = (event: MouseEvent) => {
+  event.preventDefault()
+  electronAPI()?.showContextMenu({ type: 'text' })
+}
+
+if (isElectron()) {
+  useEventListener(terminalEl, 'contextmenu', showContextMenu)
+}
+
+onMounted(() => {
+  selectionDisposable = terminal.onSelectionChange(() => {
+    hasSelection.value = terminal.hasSelection()
+  })
+})
+
+onUnmounted(() => {
+  selectionDisposable?.dispose()
+  emit('unmounted')
+})
+</script>
+
+<style scoped>
+@reference '../../../../assets/css/style.css';
+
+:deep(.p-terminal) .xterm {
+  @apply overflow-hidden;
+}
+
+:deep(.p-terminal) .xterm-screen {
+  @apply bg-neutral-900 overflow-hidden;
+}
+</style>