fix: Add InteractionLogger to plugin ServerContext to fix session-resume phase reset

Without InteractionLogger, hasInteractions() always returned false, causing
isFirstCallFromInitialState() to return true on every new OpenCode session.
This made WhatsNextHandler auto-transition back to the first phase (explore)
on each plugin load, ignoring the phase stored on disk.

Add InteractionLogger using the same FileStorage instance as ConversationManager,
matching how server-config.ts wires the MCP server.

Author: mrsimpson