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/maintenance/TerminalOutputDrawer.vue

@@ -0,0 +1,62 @@
+<template>
+  <Drawer
+    v-model:visible="terminalVisible"
+    :header
+    position="bottom"
+    style="height: max(50vh, 34rem)"
+  >
+    <BaseTerminal @created="terminalCreated" @unmounted="terminalUnmounted" />
+  </Drawer>
+</template>
+
+<script setup lang="ts">
+import type { Terminal } from '@xterm/xterm'
+import Drawer from 'primevue/drawer'
+import type { Ref } from 'vue'
+import { onMounted } from 'vue'
+
+import BaseTerminal from '@/components/bottomPanel/tabs/terminal/BaseTerminal.vue'
+import type { useTerminal } from '@/composables/bottomPanelTabs/useTerminal'
+import { useTerminalBuffer } from '@/composables/bottomPanelTabs/useTerminalBuffer'
+import { electronAPI } from '@/utils/envUtil'
+
+// Model
+const terminalVisible = defineModel<boolean>({ required: true })
+const props = defineProps<{
+  header: string
+  defaultMessage: string
+}>()
+
+const electron = electronAPI()
+
+/** The actual output of all terminal commands - not rendered */
+const buffer = useTerminalBuffer()
+let xterm: Terminal | null = null
+
+// Created and destroyed with the Drawer - contents copied from hidden buffer
+const terminalCreated = (
+  { terminal, useAutoSize }: ReturnType<typeof useTerminal>,
+  root: Ref<HTMLElement | undefined>
+) => {
+  xterm = terminal
+  useAutoSize({ root, autoRows: true, autoCols: true })
+  terminal.write(props.defaultMessage)
+  buffer.copyTo(terminal)
+
+  terminal.options.cursorBlink = false
+  terminal.options.cursorStyle = 'bar'
+  terminal.options.cursorInactiveStyle = 'bar'
+  terminal.options.disableStdin = true
+}
+
+const terminalUnmounted = () => {
+  xterm = null
+}
+
+onMounted(async () => {
+  electron.onLogMessage((message: string) => {
+    buffer.write(message)
+    xterm?.write(message)
+  })
+})
+</script>