Remove dead tool_router field (rmcp 1.8 macro change)

[getappz]

Summary

The rmcp 0.16 -> 1.8.0 upgrade made the tool_router: ToolRouter<Self> field
on AgentflareMcp dead code, producing:

warning: field `tool_router` is never read
  --> src/mcp_server.rs:36

Root cause

In rmcp 0.16, #[tool_handler]'s generated list_tools/call_tool methods
read the struct's tool_router field directly. In rmcp 1.8.0 the generated
code instead calls the associated function Self::tool_router() (produced by
#[tool_router]), never touching the field. Verified against the real macro
source at rmcp-macros-1.8.0/src/tool_handler.rs:22.

Fix

Since AgentflareMcp had no other fields, it's now a unit struct:

#[derive(Clone)]
pub struct AgentflareMcp;

new() was removed (nothing left to initialize) and the ~9 call sites
(AgentflareMcp::new() in run() and tests) were updated to construct the
unit struct directly (AgentflareMcp). The now-unused ToolRouter import was
dropped too.

Test plan

• cargo build — the tool_router warning is gone; only the
  pre-existing optimize::RouteContext dead-field warning remains.
• cargo test -- --test-threads=1 — 94/94 pass.
• E2E stdio dispatch through the macro-generated router (tools/list
  returns both check_session_health and get_routing_suggestion;
  tools/call get_routing_suggestion returns a cheap-model suggestion).