[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/FeatureControlConfiguration.swift

@@ -0,0 +1,33 @@
+import Foundation
+
+/// Wiring for one Atomenta Feature Control module deployment.
+public struct FeatureControlConfiguration: Sendable {
+    public var baseURL: String
+    public var evaluatePath: String
+    public var notificationsPath: String
+    public var telemetryPath: String
+    public var environment: String
+    public var auth: any FeatureControlAuthorizing
+    /// In-memory cache TTL. FC-060 §5 recommends 30–60s client-side.
+    public var cacheTTL: TimeInterval
+    /// FC-060 §5 recommends 1.5–3s at the BFF; same budget applies here.
+    public var requestTimeout: TimeInterval
+
+    public init(baseURL: String,
+                environment: String,
+                auth: any FeatureControlAuthorizing,
+                evaluatePath: String = "/api/feature-control/evaluate",
+                notificationsPath: String = "/api/feature-control/notifications",
+                telemetryPath: String = "/api/feature-control/telemetry/exposure",
+                cacheTTL: TimeInterval = 45,
+                requestTimeout: TimeInterval = 3) {
+        self.baseURL = baseURL
+        self.environment = environment
+        self.auth = auth
+        self.evaluatePath = evaluatePath
+        self.notificationsPath = notificationsPath
+        self.telemetryPath = telemetryPath
+        self.cacheTTL = cacheTTL
+        self.requestTimeout = requestTimeout
+    }
+}