Add DAP Proxies and Utilities implementors page

[wolf]

A new category for the DAP ecosystem

The three existing implementors pages cover the obvious cases: adapters that wrap debuggers, editors that speak DAP as a client, and libraries for building either. But there's a fourth kind of thing emerging — tools that sit between adapters and clients, routing or multiplexing the protocol without being either one.

dap-mux is the first entry in a new page I'm proposing for exactly this category.

What dap-mux does

dap-mux is a DAP proxy. It sits between a debug adapter and multiple clients, so you can connect your editor and a REPL to the same debug session simultaneously. Both clients are first-class — either can set breakpoints, step, evaluate expressions. A client that joins late gets the current session state replayed to it immediately.

This isn't a feature any adapter or editor is positioned to provide. It's infrastructure for composing DAP tools freely — any editor, any language, any adapter.

Why a new page, not an existing one

dap-mux isn't a debug adapter — its own README says so explicitly. It doesn't belong in the adapters list any more than a load balancer belongs in a list of web servers. The tools and SDKs pages don't fit either.

The right answer is a new category: tools that route, multiplex, or observe DAP traffic. I've called it "Proxies and Utilities."

The ecosystem is already growing

@shaleh has built dap-observer, a read-only DAP client that connects to a running dap-mux session and renders the current frame's variables as a navigable terminal tree. It's already the second entry on the new page.

Two tools in this space within the first month of dap-mux being public. The category is real and worth having a home in the implementors section.

[wolf]

@microsoft-github-policy-service agree

[wolf]

Just tagging @shaleh so that he can see I made this PR