Migrate to YAW/2 protocol: WebRTC transport, anchor signaling, nacl/box crypto

Replace the original raw-TCP peer connections and Blowfish/RSA-era design with
the YAW/2 protocol stack:

Transport
- internal/mesh/peer.go: raw TCP + manual ECDH replaced with pion/webrtc
  DataChannels (ICE, DTLS, SCTP). Peers negotiate via sealed offer/answer/
  candidate exchange rather than direct dialling.
- internal/nat: deleted — ICE subsumes everything this package was going to do.

Signaling
- cmd/anchor: new WebSocket signaling server (replaces cmd/relay). Verifies
  Ed25519 challenge/join signatures, routes opaque nacl/box blobs, broadcasts
  peer-join/peer-leave events. Never sees plaintext signaling content.
- internal/anchor: new anchor client. Manages PeerConnection lifecycle,
  decides offerer by peer-id comparison, seals/opens signaling payloads with
  nacl/box, implements mesh.Anchor.

Crypto (internal/crypto)
- PeerID encoding: base64url → lowercase hex (64 chars, YAW/2 §2).
- Sign/Verify: hex signatures throughout.
- Added CurvePublicKey/CurvePrivateKey: X25519 keys derived from Ed25519
  identity via Montgomery conversion (filippo.io/edwards25519), matching
  libsodium's crypto_sign_ed25519_*_to_curve25519.
- Added SignalingBox/SignalingOpen: nacl/box (XSalsa20-Poly1305) seal/open
  for signaling payloads.

Wire types (internal/proto)
- ChatMessage gains Mid (random 16-byte hex) for mesh deduplication (§8).
- FileChunk removed from PeerMessage — chunks go on a separate binary
  DataChannel labelled "f:<xid>"; FileDone added.
- New types: SignalingPayload, AnchorMessage, HelloMessage, HelloBindString.
- PeerID.Short() now returns first 16 hex chars grouped in 4s.
- IPC: CmdConnect removed; CmdJoinNetwork/CmdLeaveNetwork added;
  EvtSessionReady added (fires when DataChannel opens and hello is received).

IPC (internal/ipc)
- join_network/leave_network replace connect (direct TCP dial).
- Network joins are context-scoped: leave_network or client disconnect
  cancels the anchor connection cleanly.

README updated to reflect new project layout, getting-started commands,
IPC protocol, and roadmap state.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

go.mod

@@ -1,10 +1,36 @@
 module github.com/waste-go
 
-go 1.22
+go 1.24.0
 
 require (
+	filippo.io/edwards25519 v1.2.0
 	github.com/google/uuid v1.6.0
 	golang.org/x/crypto v0.24.0
+	nhooyr.io/websocket v1.8.17
 )
 
-require golang.org/x/sys v0.21.0 // indirect
+require (
+	github.com/davecgh/go-spew v1.1.1 // indirect
+	github.com/pion/datachannel v1.5.8 // indirect
+	github.com/pion/dtls/v2 v2.2.12 // indirect
+	github.com/pion/ice/v2 v2.3.38 // indirect
+	github.com/pion/interceptor v0.1.29 // indirect
+	github.com/pion/logging v0.2.2 // indirect
+	github.com/pion/mdns v0.0.12 // indirect
+	github.com/pion/randutil v0.1.0 // indirect
+	github.com/pion/rtcp v1.2.14 // indirect
+	github.com/pion/rtp v1.8.7 // indirect
+	github.com/pion/sctp v1.8.19 // indirect
+	github.com/pion/sdp/v3 v3.0.9 // indirect
+	github.com/pion/srtp/v2 v2.0.20 // indirect
+	github.com/pion/stun v0.6.1 // indirect
+	github.com/pion/transport/v2 v2.2.10 // indirect
+	github.com/pion/turn/v2 v2.1.6 // indirect
+	github.com/pion/webrtc/v3 v3.3.6 // indirect
+	github.com/pmezard/go-difflib v1.0.0 // indirect
+	github.com/stretchr/testify v1.9.0 // indirect
+	github.com/wlynxg/anet v0.0.3 // indirect
+	golang.org/x/net v0.22.0 // indirect
+	golang.org/x/sys v0.21.0 // indirect
+	gopkg.in/yaml.v3 v3.0.1 // indirect
+)