Add dashboard metrics, activity log, and dark theme

- Add DashboardMetrics for tracking downloads/uploads/cache hits per registry
- Add ActivityLog for recent activity with bounded size (50 entries)
- Instrument Docker, npm, Maven, and Cargo handlers with metrics
- Add /api/ui/dashboard endpoint with global stats and activity
- Implement dark theme dashboard with real-time polling (5s interval)
- Add mount points table showing registry paths and proxy upstreams

nora-registry/src/activity_log.rs

@@ -0,0 +1,103 @@
+use chrono::{DateTime, Utc};
+use parking_lot::RwLock;
+use serde::Serialize;
+use std::collections::VecDeque;
+
+/// Type of action that was performed
+#[derive(Debug, Clone, Serialize, PartialEq)]
+pub enum ActionType {
+    Pull,
+    Push,
+    CacheHit,
+    ProxyFetch,
+}
+
+impl std::fmt::Display for ActionType {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            ActionType::Pull => write!(f, "PULL"),
+            ActionType::Push => write!(f, "PUSH"),
+            ActionType::CacheHit => write!(f, "CACHE"),
+            ActionType::ProxyFetch => write!(f, "PROXY"),
+        }
+    }
+}
+
+/// A single activity log entry
+#[derive(Debug, Clone, Serialize)]
+pub struct ActivityEntry {
+    pub timestamp: DateTime<Utc>,
+    pub action: ActionType,
+    pub artifact: String,
+    pub registry: String,
+    pub source: String, // "LOCAL", "PROXY", "CACHE"
+}
+
+impl ActivityEntry {
+    pub fn new(action: ActionType, artifact: String, registry: &str, source: &str) -> Self {
+        Self {
+            timestamp: Utc::now(),
+            action,
+            artifact,
+            registry: registry.to_string(),
+            source: source.to_string(),
+        }
+    }
+}
+
+/// Thread-safe activity log with bounded size
+pub struct ActivityLog {
+    entries: RwLock<VecDeque<ActivityEntry>>,
+    max_entries: usize,
+}
+
+impl ActivityLog {
+    pub fn new(max: usize) -> Self {
+        Self {
+            entries: RwLock::new(VecDeque::with_capacity(max)),
+            max_entries: max,
+        }
+    }
+
+    /// Add a new entry to the log, removing oldest if at capacity
+    pub fn push(&self, entry: ActivityEntry) {
+        let mut entries = self.entries.write();
+        if entries.len() >= self.max_entries {
+            entries.pop_front();
+        }
+        entries.push_back(entry);
+    }
+
+    /// Get the most recent N entries (newest first)
+    pub fn recent(&self, count: usize) -> Vec<ActivityEntry> {
+        let entries = self.entries.read();
+        entries
+            .iter()
+            .rev()
+            .take(count)
+            .cloned()
+            .collect()
+    }
+
+    /// Get all entries (newest first)
+    pub fn all(&self) -> Vec<ActivityEntry> {
+        let entries = self.entries.read();
+        entries.iter().rev().cloned().collect()
+    }
+
+    /// Get the total number of entries
+    pub fn len(&self) -> usize {
+        self.entries.read().len()
+    }
+
+    /// Check if the log is empty
+    pub fn is_empty(&self) -> bool {
+        self.entries.read().is_empty()
+    }
+}
+
+impl Default for ActivityLog {
+    fn default() -> Self {
+        Self::new(50)
+    }
+}