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, 46 insertions, 0 deletions

diff --git a/octosentry/PersistenceStore.swift b/octosentry/PersistenceStore.swift
new file mode 100644
index 0000000..ca86eec
--- /dev/null
+++ b/octosentry/PersistenceStore.swift
@@ -0,0 +1,46 @@
+//
+//  PersistenceStore.swift
+//  octosentry
+//
+//  Loads and saves PersistedState as JSON in the app's Application Support
+//  container. No entitlement needed — sandboxed apps always get a private
+//  Application Support directory in their own container.
+//
+
+import Foundation
+
+actor PersistenceStore {
+    private let fileURL: URL
+
+    private static let decoder: JSONDecoder = {
+        let decoder = JSONDecoder()
+        decoder.dateDecodingStrategy = .iso8601
+        return decoder
+    }()
+
+    private static let encoder: JSONEncoder = {
+        let encoder = JSONEncoder()
+        encoder.dateEncodingStrategy = .iso8601
+        return encoder
+    }()
+
+    init() {
+        let appSupport = FileManager.default.urls(for: .applicationSupportDirectory, in: .userDomainMask)[0]
+        let directory = appSupport.appendingPathComponent("octosentry", isDirectory: true)
+        try? FileManager.default.createDirectory(at: directory, withIntermediateDirectories: true)
+        fileURL = directory.appendingPathComponent("state.json")
+    }
+
+    func load() -> PersistedState {
+        guard let data = try? Data(contentsOf: fileURL),
+              let state = try? Self.decoder.decode(PersistedState.self, from: data) else {
+            return .placeholder
+        }
+        return state
+    }
+
+    func save(_ state: PersistedState) {
+        guard let data = try? Self.encoder.encode(state) else { return }
+        try? data.write(to: fileURL, options: .atomic)
+    }
+}