Doormile AI: replace the bot popover with a right-side slide-over

Renames the operator assistant to "Doormile AI / Operations Copilot" and
moves it from a header Popover to a portalled slide-over panel.

- DoormileAI/ — trigger, panel, welcome, message, composer and shared
  primitives. Assistant turns are deliberately NOT bubbles; that is what
  keeps this reading as part of the dashboard rather than a bolted-on
  chatbot.
- pageContext.js — route-aware suggested questions. Every suggestion is a
  phrasing the matcher actually resolves; a chip that returns "I can't
  answer that" is worse than no chip.
- DoormileAI.css — panel styling, animation, responsive and reduced-motion.
  Selectors that style an Astryx Stack are written `.dai-root .x` because
  `padding={0}` emits a StyleX atomic at the same specificity as a bare
  class, so a single class can lose on stylesheet order.
- Messages are JSON round-tripped through localStorage, so icons are
  referenced by key rather than stored as React elements — an element does
  not survive the trip and the rehydrated value crashes the next render.
- Errors now render a polished state and log the real error to the console,
  instead of surfacing raw API messages in a toast.

The route, sidebar entry and i18n key for the old standalone Assistant page
are removed with it — this is a header surface, not a page.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/utils/locales/en.json

@@ -17,7 +17,6 @@
   "profitability": "Profitability",
   "dispatch": "Dispatch",
   "customers": "Customers",
-  "assistant": "Assistant",
   "fleetops": "Fleet & Ops",
   "hubs": "Hubs",
   "vehicles": "Vehicles",