Use consistent plain-language snapshot reasons

mac/Sources/Byre/Changes.swift

@@ -371,7 +371,7 @@ private struct SnapWhere: View {
         HStack(spacing: 0) {
             Text("snapshot #\(n)")
             if let snap {
-                Text(" · \(snap.trigger.rawValue) · \(clockText(snap.createdAt))")
+                Text(" · \(snap.reason) · \(clockText(snap.createdAt))")
             }
             Text(" · ")
             step(n - 1, "← #\(n - 1)", snaps)

mac/Sources/Byre/Chat.swift

@@ -1929,7 +1929,7 @@ private struct SnapshotRow: View {
         }
         .font(Fonts.font(11))
         .foregroundStyle(Palette.muted)
-        .help("\(snap.trigger.rawValue.replacingOccurrences(of: "_", with: " ")) · \(time)")
+        .help("\(snap.reason) · \(time)")
     }
 
 }

mac/Sources/Byre/Format.swift

@@ -165,6 +165,21 @@ func isoText(_ date: Date) -> String {
     date.formatted(Date.ISO8601FormatStyle(includingFractionalSeconds: true))
 }
 
+extension Snapshot {
+    var reason: String {
+        switch trigger {
+        case .message: "agent message"
+        case .turnEnd: "turn ended"
+        case .toolCall: "tool call"
+        case .askHuman: "question asked"
+        case .timer: "periodic snapshot"
+        case .requested: "snapshot requested"
+        case .answer: "before delivering an answer"
+        case .fork: "before forking"
+        }
+    }
+}
+
 func clockText(_ d: Date) -> String {
     d.formatted(Date.VerbatimFormatStyle(format: "\(hour: .twoDigits(clock: .twentyFourHour, hourCycle: .zeroBased)):\(minute: .twoDigits):\(second: .twoDigits)", timeZone: .current, calendar: .current))
 }