feat(workspace): add voice-friendly agent names to headers, lists and operator tools #816

Add an opt-in Agent names setting so an external voice operator can say “Send a prompt to Apollo” and reliably identify the intended agent. Use the user's approved ranked list of 100 names, beginning with Apollo, Jasper and Beatrix.

Acceptance:

• Default off; enabling assigns stable names to existing/new provider agents without changing titles, prompts, focus or layout. Disabling hides names and name lookup, retaining assignments for re-enable.
• Names are allocated once across application windows, retained across restart, reload/provider replacement and restore, with distinct names for genuinely new/duplicated agents. Do not silently recycle a closed agent's spoken address. Beyond the pool, use explicit numeric suffixes.
• Show a prominent readable name beside the title in structured and native agent headers, and in the Dispatch agent list, including tiled layouts. Shell terminals do not get names.
• External operator MCP observations/search expose the same enabled names and documented name-to-stable-ID lookup, preserving ambiguity/unavailable-window checks. Sending still targets stable IDs; disabling the feature does not disable the operator server.
• Keep allocation isolated from MCP and from opaque workspace persistence, preserve current panes/conversation, and verify allocation durability/concurrency, replacement continuity, toggle visibility and actual search/UI contracts.

Implementation on a dedicated plan-first feature branch; no merge authorization for this new feature is assumed from #812's completed workflow.