Voice dictation: add toggle mode (press-to-start, press-to-stop)

Feature Request

Current behavior: Voice dictation only supports push-to-hold (voice:pushToTalk) — you must hold a key the entire time you're speaking.

Problem: For multi-sentence dictation, holding a key continuously is ergonomically painful and interrupts natural speech flow.

Requested behavior: Add a toggle mode — press once to start recording, press again to stop. This would be a new keybinding action (e.g., voice:toggleRecord) alongside the existing voice:pushToTalk.

Example keybinding:

{
  "bindings": [
    {
      "context": "Chat",
      "bindings": {
        "meta+k": "voice:toggleRecord"
      }
    }
  ]
}

Why this matters: Voice input is great for quick commands, but for longer dictation (task descriptions, debriefs, brainstorming), push-to-hold makes it impractical. Toggle mode would make voice a viable primary input method.