Loki Mode

Dashboard polish: a calmer, more readable live view

Fixes from watching the live dashboard during a real build, all aimed at a
cleaner experience for whoever is watching:

• Markdown is now rendered as a formatted preview, not raw text. The Spec panel
  (your generated spec), the wiki sections, the How-to-Run / USAGE view, task
  descriptions, and handoff/escalation notes now show headings, lists, bold, and
  code blocks instead of literal #, **, and ``` markers. The renderer escapes its
  input first, so a spec or wiki body can never inject script.
• The model picker no longer slams shut. A background refresh used to re-render
  the dropdown out from under you mid-selection; it now stays open while you
  choose.
• Keyboard shortcuts are removed. Typing in any text box used to trigger
  app actions (switching tabs, toggling the theme); the dashboard no longer binds
  app-level hotkeys, so typing only types.
• Dark mode is removed; the dashboard is light-only. The previous dark palette
  looked worse and an OS dark preference no longer flips it.
• The dashboard no longer lingers after you stop your last run. When you press
  Stop and no other run is active, a dashboard that was auto-started with a run
  shuts itself down; a dashboard you started yourself with loki dashboard stays
  up and shows a clear "no active runs" note. It never tears down a dashboard that
  other running projects still need.