Add persistence, multi-repo watch list, and background polling0.3.0

Closes #1-#5 (milestones 0.2.0, 0.3.0).

- Flat JSON persistence (PersistedState/PersistenceStore) in Application
  Support, chosen over SwiftData since the dataset is small and the
  existing model types are plain Codable value types passed across actor
  boundaries.
- Repo watch list, per-event seen-state, and last-fetch timestamps are
  now persisted instead of living only in memory.
- Configurable minimum severity filter, applied from a cached raw fetch
  so changing it doesn't require a network round-trip.
- Multi-repo support: SecurityEventStore now loops over a persisted watch
  list instead of one hardcoded repo, with an in-popover UI (gear button)
  to add/remove repos.
- Background polling every 15 minutes, layered on top of the existing
  refresh-on-open and manual refresh, so the feed stays fresh even while
  the popover is closed.

1 files changed, 100 insertions, 5 deletions

diff --git a/octosentry/SecurityEventListView.swift b/octosentry/SecurityEventListView.swift
index 4542275..a5dba3e 100644
--- a/octosentry/SecurityEventListView.swift
+++ b/octosentry/SecurityEventListView.swift
@@ -8,16 +8,22 @@ import SwiftUI
 
 struct SecurityEventListView: View {
     var store: SecurityEventStore
+    @State private var showingRepoManager = false
 
     var body: some View {
         VStack(alignment: .leading, spacing: 0) {
             header
             Divider()
-            content
+            if showingRepoManager {
+                RepoManagerView(store: store)
+            } else {
+                content
+            }
         }
         .frame(width: 380, height: 420)
         .task {
             await store.refresh()
+            store.startPolling()
         }
     }
 
@@ -33,13 +39,34 @@ struct SecurityEventListView: View {
 
             Spacer()
 
+            if !showingRepoManager {
+                Picker("Minimum severity", selection: Binding(
+                    get: { store.minimumSeverity },
+                    set: { newValue in Task { await store.setMinimumSeverity(newValue) } }
+                )) {
+                    ForEach(SecurityEventSeverity.allCases, id: \.self) { severity in
+                        Text(severity.displayName).tag(severity)
+                    }
+                }
+                .pickerStyle(.menu)
+                .labelsHidden()
+                .fixedSize()
+
+                Button {
+                    Task { await store.refresh() }
+                } label: {
+                    Image(systemName: "arrow.clockwise")
+                }
+                .buttonStyle(.plain)
+                .disabled(store.isLoading)
+            }
+
             Button {
-                Task { await store.refresh() }
+                showingRepoManager.toggle()
             } label: {
-                Image(systemName: "arrow.clockwise")
+                Image(systemName: showingRepoManager ? "xmark.circle" : "gearshape")
             }
             .buttonStyle(.plain)
-            .disabled(store.isLoading)
 
             Button("Quit") {
                 NSApplication.shared.terminate(nil)
@@ -56,7 +83,15 @@ struct SecurityEventListView: View {
             StatusView(systemImage: "exclamationmark.triangle", tint: .orange, message: store.errorMessages.joined(separator: "\n\n"))
         } else if store.events.isEmpty && !store.isLoading {
             VStack(spacing: 8) {
-                StatusView(systemImage: "checkmark.shield", tint: .green, message: "No open security alerts")
+                if store.totalFetchedCount > 0 {
+                    StatusView(
+                        systemImage: "line.3.horizontal.decrease.circle",
+                        tint: .secondary,
+                        message: "\(store.totalFetchedCount) alert(s) are below your minimum severity filter"
+                    )
+                } else {
+                    StatusView(systemImage: "checkmark.shield", tint: .green, message: "No open security alerts")
+                }
                 if !store.unavailableNotices.isEmpty {
                     NoticeBanner(messages: store.unavailableNotices)
                         .padding(.horizontal)
@@ -84,6 +119,66 @@ struct SecurityEventListView: View {
     }
 }
 
+private struct RepoManagerView: View {
+    var store: SecurityEventStore
+    @State private var newRepoText = ""
+
+    var body: some View {
+        VStack(alignment: .leading, spacing: 10) {
+            Text("Watched Repositories")
+                .font(.subheadline.weight(.semibold))
+
+            if store.watchedRepos.isEmpty {
+                Text("No repos watched yet.")
+                    .font(.callout)
+                    .foregroundStyle(.secondary)
+            } else {
+                ForEach(store.watchedRepos, id: \.self) { repo in
+                    HStack {
+                        Text(repo)
+                            .font(.callout)
+                        Spacer()
+                        Button {
+                            Task { await store.removeRepo(repo) }
+                        } label: {
+                            Image(systemName: "minus.circle.fill")
+                                .foregroundStyle(.red)
+                        }
+                        .buttonStyle(.plain)
+                    }
+                }
+            }
+
+            Divider()
+
+            HStack {
+                TextField("owner/repo", text: $newRepoText)
+                    .textFieldStyle(.roundedBorder)
+                    .onSubmit(addRepo)
+
+                Button("Add", action: addRepo)
+                    .disabled(newRepoText.trimmingCharacters(in: .whitespacesAndNewlines).isEmpty)
+            }
+
+            if let errorMessage = store.watchListErrorMessage {
+                Text(errorMessage)
+                    .font(.caption2)
+                    .foregroundStyle(.red)
+            }
+
+            Spacer()
+        }
+        .padding(12)
+        .frame(maxWidth: .infinity, alignment: .leading)
+    }
+
+    private func addRepo() {
+        let text = newRepoText
+        newRepoText = ""
+        Task { await store.addRepo(text) }
+    }
+}
+
 private struct ErrorBanner: View {
     let messages: [String]