feat: Sprint 7 — Go SDK with QUIC transport and Cap'n Proto RPC

First non-Rust client SDK for quicproquo ecosystem.

- Cap'n Proto codegen: generated 6487-line Go types from node.capnp
  with all 24 RPC methods (NodeService, Auth, Envelope)
- QUIC transport: quic-go + TLS 1.3, ALPN "capnp", single bidi stream,
  300s idle timeout, InsecureSkipVerify for dev, custom CA cert support
- High-level qpq package: Connect, Health, ResolveUser, CreateChannel,
  Send/SendWithTTL, Receive/ReceiveWait, DeleteAccount, OPAQUE wrappers
- Auth management: session token storage, version/token/deviceID on all RPCs
- Example program and README with API reference

All tests pass: go test ./..., go vet, go build

sdks/go/go.sum

@@ -0,0 +1,16 @@
+capnproto.org/go/capnp/v3 v3.1.0-alpha.2 h1:93ISpqHf2/3WQlfrBP0tT8Dg/RQc3uq6DV36vN0ePWk=
+capnproto.org/go/capnp/v3 v3.1.0-alpha.2/go.mod h1:2vT5D2dtG8sJGEoEKU17e+j7shdaYp1Myl8X03B3hmc=
+github.com/colega/zeropool v0.0.0-20230505084239-6fb4a4f75381 h1:d5EKgQfRQvO97jnISfR89AiCCCJMwMFoSxUiU0OGCRU=
+github.com/colega/zeropool v0.0.0-20230505084239-6fb4a4f75381/go.mod h1:OU76gHeRo8xrzGJU3F3I1CqX1ekM8dfJw0+wPeMwnp0=
+github.com/quic-go/quic-go v0.59.0 h1:OLJkp1Mlm/aS7dpKgTc6cnpynnD2Xg7C1pwL6vy/SAw=
+github.com/quic-go/quic-go v0.59.0/go.mod h1:upnsH4Ju1YkqpLXC305eW3yDZ4NfnNbmQRCMWS58IKU=
+golang.org/x/crypto v0.41.0 h1:WKYxWedPGCTVVl5+WHSSrOBT0O8lx32+zxmHxijgXp4=
+golang.org/x/crypto v0.41.0/go.mod h1:pO5AFd7FA68rFak7rOAGVuygIISepHftHnr8dr6+sUc=
+golang.org/x/net v0.43.0 h1:lat02VYK2j4aLzMzecihNvTlJNQUq316m2Mr9rnM6YE=
+golang.org/x/net v0.43.0/go.mod h1:vhO1fvI4dGsIjh73sWfUVjj3N7CA9WkKJNQm2svM6Jg=
+golang.org/x/sync v0.7.0 h1:YsImfSBoP9QPYL0xyKJPq0gcaJdG3rInoqxTWbfQu9M=
+golang.org/x/sync v0.7.0/go.mod h1:Czt+wKu1gCyEFDUtn0jG5QVvpJ6rzVqr5aXyt9drQfk=
+golang.org/x/sync v0.16.0 h1:ycBJEhp9p4vXvUZNszeOq0kGTPghopOL8q0fq3vstxw=
+golang.org/x/sync v0.16.0/go.mod h1:1dzgHSNfp02xaA81J2MS99Qcpr2w7fw1gpm99rleRqA=
+golang.org/x/sys v0.35.0 h1:vz1N37gP5bs89s7He8XuIYXpyY0+QlsKmzipCbUtyxI=
+golang.org/x/sys v0.35.0/go.mod h1:BJP2sWEmIv4KK5OTEluFJCKSidICx8ciO85XgH3Ak8k=