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.

crates/quicprochat-server/src/metrics.rs

@@ -0,0 +1,64 @@
+//! Prometheus metrics for the server.
+//!
+//! All counters/histograms/gauges use the `metrics` crate and are exported
+//! via metrics-exporter-prometheus on a configurable HTTP port (e.g. /metrics).
+
+/// Record one enqueue (success). Call after a message is enqueued.
+pub fn record_enqueue_total() {
+    metrics::counter!("enqueue_total").increment(1);
+}
+
+/// Record enqueued payload size in bytes.
+pub fn record_enqueue_bytes(bytes: u64) {
+    metrics::counter!("enqueue_bytes_total").increment(bytes);
+}
+
+/// Record one fetch (success). Call when fetch returns.
+pub fn record_fetch_total() {
+    metrics::counter!("fetch_total").increment(1);
+}
+
+/// Record one fetch_wait (success). Call when fetch_wait returns.
+pub fn record_fetch_wait_total() {
+    metrics::counter!("fetch_wait_total").increment(1);
+}
+
+/// Set the delivery queue depth gauge (sample). Updated at enqueue/fetch time.
+pub fn record_delivery_queue_depth(depth: usize) {
+    metrics::gauge!("delivery_queue_depth").set(depth as f64);
+}
+
+/// Record one KeyPackage upload (success).
+pub fn record_key_package_upload_total() {
+    metrics::counter!("key_package_upload_total").increment(1);
+}
+
+/// Record successful auth login (session token issued).
+pub fn record_auth_login_success_total() {
+    metrics::counter!("auth_login_success_total").increment(1);
+}
+
+/// Record failed auth login attempt.
+pub fn record_auth_login_failure_total() {
+    metrics::counter!("auth_login_failure_total").increment(1);
+}
+
+/// Record rate limit hit (enqueue rejected).
+pub fn record_rate_limit_hit_total() {
+    metrics::counter!("rate_limit_hit_total").increment(1);
+}
+
+// ── Storage operation latency ───────────────────────────────────────────────
+
+/// Record storage operation latency. Called by instrumented Store wrappers.
+pub fn record_storage_latency(operation: &'static str, duration: std::time::Duration) {
+    metrics::histogram!("storage_operation_duration_seconds", "op" => operation)
+        .record(duration.as_secs_f64());
+}
+
+// ── Server info ────────────────────────────────────────────────────────────
+
+/// Record the server uptime in seconds (set periodically).
+pub fn record_uptime_seconds(secs: f64) {
+    metrics::gauge!("server_uptime_seconds").set(secs);
+}