feat: v2 Phase 1 — foundation, proto schemas, RPC framework, SDK skeleton

New workspace structure with 9 crates. Adds:

- proto/qpq/v1/*.proto: 11 protobuf schemas covering all 33 RPC methods
- quicproquo-proto: dual codegen (capnp legacy + prost v2)
- quicproquo-rpc: QUIC RPC framework (framing, server, client, middleware)
- quicproquo-sdk: client SDK (QpqClient, events, conversation store)
- quicproquo-server/domain/: protocol-agnostic domain types and services
- justfile: build commands

Wire format: [method_id:u16][req_id:u32][len:u32][protobuf] per QUIC stream.
All 151 existing tests pass. Backward compatible with v1 capnp code.

crates/quicproquo-sdk/Cargo.toml

@@ -0,0 +1,32 @@
+[package]
+name = "quicproquo-sdk"
+version = "0.1.0"
+edition = "2021"
+description = "Client SDK for quicproquo v2 — connect, auth, send, receive, subscribe"
+
+[dependencies]
+quicproquo-core  = { path = "../quicproquo-core" }
+quicproquo-proto = { path = "../quicproquo-proto" }
+quicproquo-rpc   = { path = "../quicproquo-rpc" }
+tokio            = { workspace = true }
+futures          = { workspace = true }
+tracing          = { workspace = true }
+thiserror        = { workspace = true }
+anyhow           = { workspace = true }
+serde            = { workspace = true }
+serde_json       = { workspace = true }
+bincode          = { workspace = true }
+hex              = { workspace = true }
+zeroize          = { workspace = true }
+rusqlite         = { workspace = true }
+argon2           = { workspace = true }
+rand             = { workspace = true }
+sha2             = { workspace = true }
+rustls           = { workspace = true }
+quinn            = { workspace = true }
+
+[dev-dependencies]
+tokio = { workspace = true, features = ["test-util"] }
+
+[lints]
+workspace = true