sustituir Crashlytics por un recolector MetricKit que no sale del dispositivo

FirebaseCrashlytics se llevaba los informes de fallo a Google. Los crashes
ya llegan a Xcode Organizer por la vía de Apple, así que el sustituto no
tiene que enviar nada: DiagnosticsCollector se suscribe a MXMetricManager,
guarda los payloads de crash, cuelgue y escritura en disco como JSON en
Application Support/Diagnostics y ahí se quedan.

- Sin código de red. Retención de 5 informes, los ficheros se marcan como
  excluidos de backup (son ayuda de depuración, no datos del usuario).
- Arranque: AppDelegate llama a DiagnosticsCollector.shared.start() en
  lugar de FirebaseApp.configure() + MobileAds.shared.start().
- Ajustes → Acerca de: "Compartir diagnósticos", visible solo cuando hay
  algo recogido. Compartir es la única forma de que un informe salga del
  iPhone, y la decide el usuario. Cadenas nuevas en los 7 idiomas.

Un recolector que guarda y no enseña sería código muerto, y uno que sube
sería el problema de antes con otro nombre; por eso guarda en local y deja
el envío como acción explícita.

Closes #51

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01F1u4K16xy7eQVtgsYNZ9Vn

PortfolioJournal/Services/DiagnosticsCollector.swift

@@ -0,0 +1,121 @@
+import Foundation
+import MetricKit
+import os
+
+/// On-device replacement for Crashlytics.
+///
+/// `MXMetricManager` hands the app a daily payload with crash, hang and
+/// disk-write diagnostics that Apple already collected for it. This collector
+/// writes those payloads to the app container as JSON and **never sends them
+/// anywhere** — no network code, no third-party SDK, no identifiers. Crash
+/// reports still reach Xcode Organizer through Apple's own pipeline, which is
+/// the channel that was actually useful about Crashlytics.
+///
+/// The user can share the stored reports from Settings; that is the only way
+/// one ever leaves the device, and it is an explicit action.
+final class DiagnosticsCollector: NSObject {
+    static let shared = DiagnosticsCollector()
+
+    /// Reports older than this are pruned on every new payload.
+    private static let retentionCount = 5
+
+    private let logger = Logger(subsystem: AppConstants.bundleIdentifier, category: "diagnostics")
+    private let fileManager = FileManager.default
+    private let dateFormatter: DateFormatter = {
+        let formatter = DateFormatter()
+        formatter.dateFormat = "yyyyMMdd-HHmmss"
+        formatter.locale = Locale(identifier: "en_US_POSIX")
+        return formatter
+    }()
+
+    private override init() {
+        super.init()
+    }
+
+    /// Subscribes to MetricKit. Safe to call more than once.
+    func start() {
+        MXMetricManager.shared.add(self)
+    }
+
+    // MARK: - Storage
+
+    /// `Application Support/Diagnostics`, created on demand.
+    private var directory: URL? {
+        guard let base = fileManager.urls(for: .applicationSupportDirectory, in: .userDomainMask).first else {
+            return nil
+        }
+        let url = base.appendingPathComponent("Diagnostics", isDirectory: true)
+        if !fileManager.fileExists(atPath: url.path) {
+            try? fileManager.createDirectory(at: url, withIntermediateDirectories: true)
+        }
+        return url
+    }
+
+    /// Stored reports, newest first. Used by Settings to offer sharing them.
+    func storedReports() -> [URL] {
+        guard let directory else { return [] }
+        let contents = (try? fileManager.contentsOfDirectory(
+            at: directory,
+            includingPropertiesForKeys: [.contentModificationDateKey]
+        )) ?? []
+        return contents
+            .filter { $0.pathExtension == "json" }
+            .sorted { lhs, rhs in
+                let l = (try? lhs.resourceValues(forKeys: [.contentModificationDateKey]).contentModificationDate) ?? .distantPast
+                let r = (try? rhs.resourceValues(forKeys: [.contentModificationDateKey]).contentModificationDate) ?? .distantPast
+                return l > r
+            }
+    }
+
+    func deleteStoredReports() {
+        for url in storedReports() {
+            try? fileManager.removeItem(at: url)
+        }
+    }
+
+    private func write(_ data: Data, prefix: String) {
+        guard let directory else { return }
+        let name = "\(prefix)-\(dateFormatter.string(from: Date())).json"
+        let url = directory.appendingPathComponent(name)
+        do {
+            try data.write(to: url, options: .atomic)
+            // Diagnostics are debugging aids, not user data: keep them out of
+            // iCloud/iTunes backups.
+            var resourceValues = URLResourceValues()
+            resourceValues.isExcludedFromBackup = true
+            var mutableURL = url
+            try? mutableURL.setResourceValues(resourceValues)
+            logger.info("Stored diagnostic report \(name, privacy: .public)")
+        } catch {
+            logger.error("Could not store diagnostic report: \(error.localizedDescription, privacy: .public)")
+        }
+        prune()
+    }
+
+    private func prune() {
+        let reports = storedReports()
+        guard reports.count > Self.retentionCount else { return }
+        for url in reports.dropFirst(Self.retentionCount) {
+            try? fileManager.removeItem(at: url)
+        }
+    }
+}
+
+// MARK: - MXMetricManagerSubscriber
+
+extension DiagnosticsCollector: MXMetricManagerSubscriber {
+    func didReceive(_ payloads: [MXMetricPayload]) {
+        for payload in payloads {
+            write(payload.jsonRepresentation(), prefix: "metrics")
+        }
+    }
+
+    func didReceive(_ payloads: [MXDiagnosticPayload]) {
+        for payload in payloads {
+            let crashes = payload.crashDiagnostics?.count ?? 0
+            let hangs = payload.hangDiagnostics?.count ?? 0
+            logger.info("Diagnostic payload: \(crashes, privacy: .public) crash(es), \(hangs, privacy: .public) hang(s)")
+            write(payload.jsonRepresentation(), prefix: "diagnostics")
+        }
+    }
+}