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.

Cargo.toml

@@ -5,16 +5,12 @@ members = [
     "crates/quicproquo-proto",
     "crates/quicproquo-plugin-api",
     "crates/quicproquo-kt",
+    "crates/quicproquo-rpc",
+    "crates/quicproquo-sdk",
     "crates/quicproquo-server",
     "crates/quicproquo-client",
-    "crates/quicproquo-bot",
-    "crates/quicproquo-gen",
-    "crates/quicproquo-gui",
-    "crates/quicproquo-mobile",
-    "crates/quicproquo-ffi",
-    # P2P crate uses iroh (~90 extra deps). Kept in the workspace so it can be
-    # referenced as an optional dependency; only compiled when the `mesh` feature
-    # is enabled on quicproquo-client.
+    # P2P crate uses iroh (~90 extra deps). Only compiled when the `mesh`
+    # feature is enabled on quicproquo-client.
     "crates/quicproquo-p2p",
 ]
 
@@ -29,7 +25,6 @@ openmls_traits     = { version = "0.2" }
 # duplicate Serialize trait versions in the dependency graph.
 tls_codec          = { version = "0.3", features = ["derive"] }
 # ml-kem 0.2 is the current stable release (FIPS 203, ML-KEM-768).
-# All three parameter sets (512/768/1024) are compiled in by default — no feature flag needed.
 ml-kem             = { version = "0.2" }
 x25519-dalek       = { version = "2", features = ["static_secrets"] }
 ed25519-dalek      = { version = "2", features = ["rand_core"] }
@@ -47,7 +42,12 @@ serde              = { version = "1", features = ["derive"] }
 serde_json         = { version = "1" }
 bincode            = { version = "1" }
 
-# ── Serialisation + RPC ───────────────────────────────────────────────────────
+# ── Serialisation (v2: protobuf) ─────────────────────────────────────────────
+prost              = { version = "0.13" }
+prost-types        = { version = "0.13" }
+prost-build        = { version = "0.13" }
+
+# ── Serialisation (v1 legacy — capnp, used by existing server/client) ────────
 capnp              = { version = "0.19" }
 capnp-rpc          = { version = "0.19" }
 
@@ -60,11 +60,15 @@ quinn-proto        = { version = "0.11" }
 rustls             = { version = "0.23", default-features = false, features = ["std", "ring"] }
 rcgen              = { version = "0.13" }
 
+# ── Middleware ────────────────────────────────────────────────────────────────
+tower              = { version = "0.5", features = ["util", "limit", "timeout"] }
+
 # ── Database ─────────────────────────────────────────────────────────────
 rusqlite           = { version = "0.31", features = ["bundled-sqlcipher"] }
 
 # ── Encoding ─────────────────────────────────────────────────────────────────
 hex                = { version = "0.4" }
+bytes              = { version = "1" }
 
 # ── Server utilities ──────────────────────────────────────────────────────────
 dashmap            = { version = "5" }