Modeled on KnowledgeView's mini-chat. Three states (closed handle,
collapsed input-only, expanded full panel). Takes over the project
conversation lifecycle from WorkspaceView (resume-or-create on mount,
delete-if-empty-and-new on unmount) and adds a restart action. Reuses
ChatPanel for expanded view and ChatInputBar for collapsed.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
