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.

justfile

@@ -0,0 +1,49 @@
+# quicproquo v2 — build commands
+
+# Default: build all workspace crates
+build:
+    cargo build --workspace
+
+# Run all tests
+test:
+    cargo test --workspace
+
+# Run core crypto tests only
+test-core:
+    cargo test -p quicproquo-core
+
+# Build proto crate (triggers prost codegen)
+proto:
+    cargo build -p quicproquo-proto
+
+# Build RPC framework
+rpc:
+    cargo build -p quicproquo-rpc
+
+# Build SDK
+sdk:
+    cargo build -p quicproquo-sdk
+
+# Build server
+server:
+    cargo build -p quicproquo-server
+
+# Build client
+client:
+    cargo build -p quicproquo-client
+
+# Check all with clippy
+lint:
+    cargo clippy --workspace -- -D warnings
+
+# Format check
+fmt:
+    cargo fmt --all -- --check
+
+# Format fix
+fmt-fix:
+    cargo fmt --all
+
+# Clean build artifacts
+clean:
+    cargo clean