Keep MCP boot diagnostics out of the chat transcript

[Hmbown]

Problem

Disconnected or failing MCP servers reserve multiple rows immediately above the composer and print raw per-server failure detail into the chat shell. That obscures the conversation and turns a recoverable integration state into visual alarm.

Acceptance criteria

• The normal chat/composer geometry is identical whether MCP servers are healthy or failing.
• A compact truthful MCP status chip remains visible in the existing Tideline footer.
• Detailed server diagnostics and retry actions remain available through /mcp, not in the transcript shell.
• Regression coverage proves a failed server neither reserves composer rows nor emits raw server/retry text into chat.

Evidence

The failing-MCP regression is implemented on fix/tideline-mcp-quiet-20260830; visual/device acceptance remains a separate launch gate.