chore: rename quicproquo → quicprochat in Rust workspace

Rename all crate directories, package names, binary names, proto
package/module paths, ALPN strings, env var prefixes, config filenames,
mDNS service names, and plugin ABI symbols from quicproquo/qpq to
quicprochat/qpc.

proto/qpc/v1/delivery.proto

@@ -0,0 +1,85 @@
+syntax = "proto3";
+package qpc.v1;
+
+// Delivery service: enqueue, fetch, peek, ack, batch (6 methods).
+// Method IDs: 200-205.
+
+message Envelope {
+  uint64 seq = 1;
+  bytes data = 2;
+}
+
+message EnqueueRequest {
+  bytes recipient_key = 1;
+  bytes payload = 2;
+  bytes channel_id = 3;
+  uint32 ttl_secs = 4;
+  // Client-generated idempotency key (16 bytes, UUID v7).
+  // Server deduplicates enqueue requests with the same message_id within a TTL window.
+  bytes message_id = 5;
+}
+
+message EnqueueResponse {
+  uint64 seq = 1;
+  bytes delivery_proof = 2;
+  // True if this was a duplicate enqueue (message_id already seen).
+  bool duplicate = 3;
+}
+
+message FetchRequest {
+  bytes recipient_key = 1;
+  bytes channel_id = 2;
+  uint32 limit = 3;
+  // Device ID for multi-device scoping. When set, the server builds
+  // a composite queue key (identity_key + device_id). Empty = bare key.
+  bytes device_id = 4;
+}
+
+message FetchResponse {
+  repeated Envelope payloads = 1;
+}
+
+message FetchWaitRequest {
+  bytes recipient_key = 1;
+  bytes channel_id = 2;
+  uint64 timeout_ms = 3;
+  uint32 limit = 4;
+  bytes device_id = 5;
+}
+
+message FetchWaitResponse {
+  repeated Envelope payloads = 1;
+}
+
+message PeekRequest {
+  bytes recipient_key = 1;
+  bytes channel_id = 2;
+  uint32 limit = 3;
+  bytes device_id = 4;
+}
+
+message PeekResponse {
+  repeated Envelope payloads = 1;
+}
+
+message AckRequest {
+  bytes recipient_key = 1;
+  bytes channel_id = 2;
+  uint64 seq_up_to = 3;
+  bytes device_id = 4;
+}
+
+message AckResponse {}
+
+message BatchEnqueueRequest {
+  repeated bytes recipient_keys = 1;
+  bytes payload = 2;
+  bytes channel_id = 3;
+  uint32 ttl_secs = 4;
+  // Client-generated idempotency key (16 bytes, UUID v7).
+  bytes message_id = 5;
+}
+
+message BatchEnqueueResponse {
+  repeated uint64 seqs = 1;
+}