[sub-spm-optional-products] Add LCECryptoKit and LCFeatureControl as optional sub-SPM products

LCEssentials installs standalone; each sub target-depends on it so linking a
sub's product always pulls LCEssentials in too, without the consumer having to
declare it separately.

- LCECryptoKit: internalized from the remote LCECryptoKitBinary git dependency
  (embedded token URL removed) into a local binaryTarget vendoring
  Frameworks/LCECryptoKit.xcframework. LCECryptoKitManager moved out of
  LCEssentials core into its own LCECryptoKitManager target/product; the
  no-op fallback for when the binary wasn't linked is gone (breaking change
  for existing consumers, see decisions/2026-09-15-sub-spm-optional-products.md).
- LCFeatureControl: new product wrapping Atomenta's Feature Control API
  (flag evaluation with TTL cache + safe-degrade fallback to defaults,
  notifications inbox, batched exposure telemetry). 45 new tests.

Sources/LCFeatureControl/FeatureControlNotification.swift

@@ -0,0 +1,65 @@
+import Foundation
+
+/// `GET /api/feature-control/notifications` `status` query filter.
+public enum FeatureControlNotificationStatus: String, Sendable {
+    case all, unread
+}
+
+/// One item from `NotificationListItem`.
+public struct FeatureControlNotification: Sendable, Equatable, Identifiable {
+    public let id: String
+    public let title: String
+    public let body: String
+    public let severity: String
+    public let createdAt: Date
+    public let read: Bool
+    public let ctaLabel: String?
+    public let ctaUrl: String?
+
+    public init(id: String, title: String, body: String, severity: String,
+                createdAt: Date, read: Bool, ctaLabel: String?, ctaUrl: String?) {
+        self.id = id
+        self.title = title
+        self.body = body
+        self.severity = severity
+        self.createdAt = createdAt
+        self.read = read
+        self.ctaLabel = ctaLabel
+        self.ctaUrl = ctaUrl
+    }
+}
+
+extension FeatureControlNotification: Decodable {
+    private enum CodingKeys: String, CodingKey {
+        case id, title, body, severity, createdAt, read, ctaLabel, ctaUrl
+    }
+
+    public init(from decoder: Decoder) throws {
+        let container = try decoder.container(keyedBy: CodingKeys.self)
+        let rawDate = try container.decode(String.self, forKey: .createdAt)
+        guard let date = FeatureControlDateParsing.parse(rawDate) else {
+            throw DecodingError.dataCorruptedError(forKey: .createdAt, in: container,
+                                                    debugDescription: "Unrecognized date format: \(rawDate)")
+        }
+        self.id = try container.decode(String.self, forKey: .id)
+        self.title = try container.decode(String.self, forKey: .title)
+        self.body = try container.decode(String.self, forKey: .body)
+        self.severity = try container.decode(String.self, forKey: .severity)
+        self.createdAt = date
+        self.read = try container.decode(Bool.self, forKey: .read)
+        self.ctaLabel = try container.decodeIfPresent(String.self, forKey: .ctaLabel)
+        self.ctaUrl = try container.decodeIfPresent(String.self, forKey: .ctaUrl)
+    }
+}
+
+/// `GET /api/feature-control/notifications` `result` shape.
+struct FeatureControlNotificationListResult: Decodable, Sendable {
+    let items: [FeatureControlNotification]
+    let nextCursor: String?
+}
+
+/// Wire envelope for the notifications list — `{error, result}`.
+struct FeatureControlNotificationListEnvelope: Decodable, Sendable {
+    let error: Bool
+    let result: FeatureControlNotificationListResult
+}