fix: persist dashboard metrics and count versions instead of repos

Metrics (downloads, uploads, cache hits) were stored in-memory only
and reset to zero on every restart. Now they persist to metrics.json
in the storage directory with:
- Load on startup from {storage_path}/metrics.json
- Background save every 30 seconds
- Final save on graceful shutdown
- Atomic writes (tmp + rename) to prevent corruption

Artifact count on dashboard now shows total tags/versions across
all registries instead of just counting unique repository names.
This matches user expectations when pushing multiple tags to the
same image (e.g. myapp:v1, myapp:v2 now shows 2, not 1).

nora-registry/src/dashboard_metrics.rs

@@ -1,8 +1,29 @@
 // Copyright (c) 2026 Volkov Pavel | DevITWay
 // SPDX-License-Identifier: MIT
 
+use serde::{Deserialize, Serialize};
+use std::path::{Path, PathBuf};
 use std::sync::atomic::{AtomicU64, Ordering};
 use std::time::Instant;
+use tracing::{info, warn};
+
+/// Serializable snapshot of metrics for persistence
+#[derive(Serialize, Deserialize, Default)]
+struct MetricsSnapshot {
+    downloads: u64,
+    uploads: u64,
+    cache_hits: u64,
+    cache_misses: u64,
+    docker_downloads: u64,
+    docker_uploads: u64,
+    npm_downloads: u64,
+    maven_downloads: u64,
+    maven_uploads: u64,
+    cargo_downloads: u64,
+    pypi_downloads: u64,
+    raw_downloads: u64,
+    raw_uploads: u64,
+}
 
 /// Dashboard metrics for tracking registry activity
 /// Uses atomic counters for thread-safe access without locks
@@ -25,6 +46,9 @@ pub struct DashboardMetrics {
     pub raw_uploads: AtomicU64,
 
     pub start_time: Instant,
+
+    /// Path to metrics.json for persistence
+    persist_path: Option<PathBuf>,
 }
 
 impl DashboardMetrics {
@@ -44,6 +68,75 @@ impl DashboardMetrics {
             raw_downloads: AtomicU64::new(0),
             raw_uploads: AtomicU64::new(0),
             start_time: Instant::now(),
+            persist_path: None,
+        }
+    }
+
+    /// Create metrics with persistence — loads existing data from metrics.json
+    pub fn with_persistence(storage_path: &str) -> Self {
+        let path = Path::new(storage_path).join("metrics.json");
+        let mut metrics = Self::new();
+        metrics.persist_path = Some(path.clone());
+
+        // Load existing metrics if file exists
+        if path.exists() {
+            match std::fs::read_to_string(&path) {
+                Ok(data) => match serde_json::from_str::<MetricsSnapshot>(&data) {
+                    Ok(snap) => {
+                        metrics.downloads = AtomicU64::new(snap.downloads);
+                        metrics.uploads = AtomicU64::new(snap.uploads);
+                        metrics.cache_hits = AtomicU64::new(snap.cache_hits);
+                        metrics.cache_misses = AtomicU64::new(snap.cache_misses);
+                        metrics.docker_downloads = AtomicU64::new(snap.docker_downloads);
+                        metrics.docker_uploads = AtomicU64::new(snap.docker_uploads);
+                        metrics.npm_downloads = AtomicU64::new(snap.npm_downloads);
+                        metrics.maven_downloads = AtomicU64::new(snap.maven_downloads);
+                        metrics.maven_uploads = AtomicU64::new(snap.maven_uploads);
+                        metrics.cargo_downloads = AtomicU64::new(snap.cargo_downloads);
+                        metrics.pypi_downloads = AtomicU64::new(snap.pypi_downloads);
+                        metrics.raw_downloads = AtomicU64::new(snap.raw_downloads);
+                        metrics.raw_uploads = AtomicU64::new(snap.raw_uploads);
+                        info!(
+                            downloads = snap.downloads,
+                            uploads = snap.uploads,
+                            "Loaded persisted metrics"
+                        );
+                    }
+                    Err(e) => warn!("Failed to parse metrics.json: {}", e),
+                },
+                Err(e) => warn!("Failed to read metrics.json: {}", e),
+            }
+        }
+
+        metrics
+    }
+
+    /// Save current metrics to disk
+    pub fn save(&self) {
+        let Some(path) = &self.persist_path else {
+            return;
+        };
+        let snap = MetricsSnapshot {
+            downloads: self.downloads.load(Ordering::Relaxed),
+            uploads: self.uploads.load(Ordering::Relaxed),
+            cache_hits: self.cache_hits.load(Ordering::Relaxed),
+            cache_misses: self.cache_misses.load(Ordering::Relaxed),
+            docker_downloads: self.docker_downloads.load(Ordering::Relaxed),
+            docker_uploads: self.docker_uploads.load(Ordering::Relaxed),
+            npm_downloads: self.npm_downloads.load(Ordering::Relaxed),
+            maven_downloads: self.maven_downloads.load(Ordering::Relaxed),
+            maven_uploads: self.maven_uploads.load(Ordering::Relaxed),
+            cargo_downloads: self.cargo_downloads.load(Ordering::Relaxed),
+            pypi_downloads: self.pypi_downloads.load(Ordering::Relaxed),
+            raw_downloads: self.raw_downloads.load(Ordering::Relaxed),
+            raw_uploads: self.raw_uploads.load(Ordering::Relaxed),
+        };
+        // Atomic write: write to tmp then rename
+        let tmp = path.with_extension("json.tmp");
+        if let Ok(data) = serde_json::to_string_pretty(&snap) {
+            if std::fs::write(&tmp, &data).is_ok() {
+                let _ = std::fs::rename(&tmp, path);
+            }
         }
     }