feat(server): v2 RPC handler dispatch for all 33 methods

Add v2_handlers module with ServerState, build_registry(), require_auth()
helper, and 33 protobuf handlers across 10 files:
- auth: 4 OPAQUE handlers (register start/finish, login start/finish)
- delivery: 6 handlers (enqueue, fetch, fetch_wait, peek, ack, batch)
- keys: 5 handlers (upload/fetch key package, upload/fetch hybrid key/keys)
- channel: create_channel
- user: resolve_user, resolve_identity
- blob: upload_blob, download_blob
- device: register, list, revoke
- p2p: publish_endpoint, resolve_endpoint, health
- federation: 6 stubs (Unimplemented)
- account: delete_account

All handlers decode protobuf, call domain services, encode response.
Auth handlers use full OPAQUE flow with session creation.
Delivery handlers include rate limiting and long-poll (fetch_wait).

crates/quicproquo-server/Cargo.toml

@@ -14,6 +14,7 @@ quicproquo-core       = { path = "../quicproquo-core" }
 quicproquo-proto      = { path = "../quicproquo-proto" }
 quicproquo-plugin-api = { path = "../quicproquo-plugin-api" }
 quicproquo-kt         = { path = "../quicproquo-kt" }
+quicproquo-rpc        = { path = "../quicproquo-rpc" }
 
 # Dynamic plugin loading
 libloading = "0.8"
@@ -21,6 +22,8 @@ libloading = "0.8"
 # Serialisation + RPC
 capnp         = { workspace = true }
 capnp-rpc     = { workspace = true }
+prost         = { workspace = true }
+bytes         = { workspace = true }
 
 # Async
 tokio         = { workspace = true }