fix(cron): surface classified run failure causes

Surface classified cron failure causes without changing raw cron JSON error text.

- add additive CLI `cause` output for finished run entries with `errorReason`
- persist/backfill full `FailoverReason` values on cron run-log entries
- thread provider context through cron finalization so provider-specific failure causes stay accurate
- extend protocol/Swift models and regression coverage for CLI JSON, run-log parsing/search, alerts, and protocol conformance

Verification:
- `pnpm lint --threads=8`
- `pnpm protocol:check`
- `pnpm exec oxfmt --check src/cli/cron-cli/shared.ts src/cli/cron-cli/shared.cause-display.test.ts src/cron/run-log.ts src/cron/run-log.error-reason.test.ts src/cron/cron-protocol-conformance.test.ts src/cron/service.failure-alert.test.ts src/cron/service/timer.ts src/cron/service/ops.ts src/gateway/protocol/schema/cron.ts scripts/protocol-gen-swift.ts`
- `git diff --check`
- AWS Crabbox `cbx_8a6a65ab83b0` / `run_42b73a4a9750`: 4 files, 20 tests passed
- autoreview clean, no accepted/actionable findings
- GitHub CI/CodeQL/OpenGrep/Workflow Sanity green/skipped/neutral on `aa29b087b2587d0aed3d409de5e7a2c706c32cdf`

Co-authored-by: Yoshikazu Terashi <yterashi@peperon-works.jp>

scripts/protocol-gen-swift.ts

@@ -47,7 +47,7 @@ const DEFAULTED_OPTIONAL_INIT_PARAMS: Record<string, Set<string>> = {
   ArtifactsGetParams: new Set(["agentId"]),
   ArtifactsDownloadParams: new Set(["agentId"]),
   MessageActionParams: new Set(["inboundTurnKind"]),
-  CronRunLogEntry: new Set(["failureNotificationDelivery"]),
+  CronRunLogEntry: new Set(["errorReason", "failureNotificationDelivery"]),
 };
 
 const header = `// Generated by scripts/protocol-gen-swift.ts — do not edit by hand\n// swiftlint:disable file_length\nimport Foundation\n\npublic let GATEWAY_PROTOCOL_VERSION = ${PROTOCOL_VERSION}\npublic let GATEWAY_MIN_PROTOCOL_VERSION = ${MIN_CLIENT_PROTOCOL_VERSION}\n\nprivate struct GatewayAnyCodingKey: CodingKey, Hashable {\n    let stringValue: String\n    let intValue: Int?\n\n    init?(stringValue: String) {\n        self.stringValue = stringValue\n        self.intValue = nil\n    }\n\n    init?(intValue: Int) {\n        self.stringValue = String(intValue)\n        self.intValue = intValue\n    }\n}\n\npublic enum ErrorCode: String, Codable, Sendable {\n${Object.values(