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/p2p.proto

@@ -0,0 +1,34 @@
+syntax = "proto3";
+package qpc.v1;
+
+// P2P endpoint publish/resolve + health (3 methods).
+// Method IDs: 800-802.
+
+message PublishEndpointRequest {
+  bytes identity_key = 1;
+  bytes node_addr = 2;
+}
+
+message PublishEndpointResponse {}
+
+message ResolveEndpointRequest {
+  bytes identity_key = 1;
+}
+
+message ResolveEndpointResponse {
+  bytes node_addr = 1;
+}
+
+message HealthRequest {}
+
+message HealthResponse {
+  string status = 1;
+  // Unique node identifier for multi-node deployments.
+  string node_id = 2;
+  // Server version string.
+  string version = 3;
+  // Uptime in seconds since process start.
+  uint64 uptime_secs = 4;
+  // Storage backend type (e.g. "sql", "file", "postgres").
+  string storage_backend = 5;
+}