Vello memory works again across the agent pipeline

The build, review, QA, respond, and rework agents can now actually read and write Vello memory — searching prior thoughts and insights for context and capturing new ones as they work. They had silently lost that ability for two reasons: the MCP server was wired up with a setting the GitHub action no longer recognizes, and the connector it launches was pinned to a version that doesn't exist — so it never started and every memory tool was missing. As a bonus, when you mention @vello its "Got it — thinking..." acknowledgment now appears within seconds instead of after a setup delay, reliably updates the same comment with the final reply, and flips that comment to a clear failure notice if the run crashes.