Wire MCP standard notifications/progress into the existing SSE stream so long-running MCP tool calls surface live progress instead of a bare spinner. A per-call progressToken maps back to (conversationId, toolCallId); ProgressAwareMcpToolCallback injects it into tools/call _meta and calls McpSyncClient directly (falling back to the delegate on error, and applying identity forwarding first). Progress events skip the ring buffer and are replayed from a latest-value snapshot on SSE reconnect. Frontend renders a gradient progress bar in ToolCallSegment when a running tool reports progress.
