feat(mcp): instrument the local MCP tool-dispatch chokepoint with PostHog events (opt-in)

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Context

Part of #6228. With the local-side telemetry wrapper module in place (companion issue), this issue wires it into packages/loopover-mcp/bin/loopover-mcp.js's --stdio tool-dispatch path.

Requirements

• Find (or create) a single chokepoint through which every registerStdioTool-registered tool's invocation passes, and call the telemetry wrapper there.
• Record: tool name, caller type ("local"), success/failure, coarse latency — same fields as the remote side, nothing more.
• Must respect the opt-in flag — if a user hasn't run loopover-mcp telemetry enable, zero data is ever sent (verify this is actually true, not just documented).
• Must not throw or block a tool response if the telemetry call fails.

Test Coverage Requirements

Match this package's existing test conventions; a regression test confirming default-off behavior sends nothing, and that a tool call succeeds normally regardless of telemetry state.

Deliverables

• Every local tool invocation triggers exactly one recordMcpToolCall when opted in, and zero when not.
• Zero behavior change to any tool's actual response.

Expected Outcome

Real usage data starts flowing for local MCP tool calls, strictly from users who've explicitly opted in.

Links & Resources

• Spec: usage-telemetry instrumentation strategy for MCP (PostHog) #6228 (parent spec)
• The local-side telemetry wrapper module issue and the telemetry enable/disable CLI-command issue (provides the opt-in flag this must respect)

[linear-code]

JSO-4326