Add appduct_list_events MCP tool

[V3RON]

Part of #95. Needs #124.

Why

MCP agents can list tools but not events, so they guess the name they pass to appduct_wait_for_event. Once the daemon keeps an event registry, they need a tool to read it.

Expected outcome

A new MCP tool, appduct_list_events({ selector?, name?, limit?, offset? }), in mcp/events-tool.ts, backed by events.list. It returns one signature line per declared event with its description, plus total. The shipped skill (skills/appduct) tells agents to list events before waiting on one.

Constraints and non-goals

• No separate describe tool; an exact name covers it.
• No event grouping.

How we know it is done

1. appduct_list_events returns signature lines with descriptions and total.
2. name: "cart.*" returns only matching events.
3. An exact name that matches one declared event also returns that event's payload_schema.
4. A session with no declared events returns an empty list and total: 0, not an error.
5. The shipped skill says to list events before waiting on one and names appduct events ls in its CLI reference.

Alternatives considered

none