control: add iroh gossip transport announcements and ec-node control CLI

evolution/proposals/ECP-0066-iroh-control-protocol.md

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+# ECP-0066: iroh-Gossip Control Protocol For Hybrid MoQ Discovery
+
+Status: Draft
+
+## Decision
+
+Add a first-party control protocol carried over iroh-gossip to advertise stream availability across multiple transport paths:
+
+- MoQ relay (WebTransport URL + broadcast name + track),
+- iroh direct (EndpointAddr + broadcast name + track).
+
+`ec-node` will expose:
+
+1. `control-announce`: publish control announcements to an iroh gossip topic.
+2. `control-listen`: subscribe to the topic and print announcements.
+3. Optional integration in `wt-publish` to announce relay-published streams via the same control topic.
+
+## Motivation
+
+We currently have two transport worlds:
+
+- relay-centric (`wt-publish`),
+- direct iroh (`moq-publish` / `moq-subscribe`).
+
+Discovery is fragmented. A shared iroh control channel makes transport selection explicit and allows consumers to discover either path (or both) from one substrate.
+
+## Scope
+
+In scope:
+
+- New control protocol data types in `ec-core`.
+- New `ControlGossip` helper in `ec-iroh`.
+- New CLI surfaces in `ec-node` for announce/listen.
+- Optional relay announcement from `wt-publish`.
+
+Out of scope:
+
+- Policy engine for automatic best-path selection.
+- Security policy beyond existing iroh/gossip trust boundaries.
+- Replacing existing catalog gossip immediately (coexist first).
+
+## Rollout / Reversibility
+
+- Additive and reversible: removing control commands and topic does not affect existing media paths.
+- Existing MoQ publish/subscribe flows continue unchanged.