Add new features and tests for AirGap and Time modules

- Introduced `SbomService` tasks documentation.
- Updated `StellaOps.sln` to include new projects: `StellaOps.AirGap.Time` and `StellaOps.AirGap.Importer`.
- Added unit tests for `BundleImportPlanner`, `DsseVerifier`, `ImportValidator`, and other components in the `StellaOps.AirGap.Importer.Tests` namespace.
- Implemented `InMemoryBundleRepositories` for testing bundle catalog and item repositories.
- Created `MerkleRootCalculator`, `RootRotationPolicy`, and `TufMetadataValidator` tests.
- Developed `StalenessCalculator` and `TimeAnchorLoader` tests in the `StellaOps.AirGap.Time.Tests` namespace.
- Added `fetch-sbomservice-deps.sh` script for offline dependency fetching.

docs/modules/scheduler/prep/2025-11-20-surface-fs-pointer.md

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+# Surface FS Pointer Contract (Draft) — PREP-SCHED-SURFACE-01
+
+Status: Draft (2025-11-20)
+Owners: Scheduler Worker Guild
+Scope: Define pointer model for Surface FS to unblock scheduler worker planning.
+
+## Pointer model
+- Identifier: `surfacefs://<tenant>/<dataset>/<version>`.
+- Fields:
+  - `tenant_id`
+  - `dataset` (e.g., `sbom`, `findings`, `reachability`)
+  - `version` (content hash or monotonic version)
+  - `storage_uri` (unset/relative in sealed mode; content-addressed path recommended)
+  - `created_at` (RFC3339 UTC)
+- Deterministic JSON serialization with sorted keys.
+
+## Scheduler usage
+- Workers receive pointer in job payload; pointer is immutable per job.
+- Cache key = `surface_fs_pointer`.
+- Validation: ensure `dataset` is allowlisted; reject untrusted storage_uri when sealed mode is on.
+
+## Open decisions
+- Final allowlist of datasets.
+- Whether inline `storage_uri` is permitted under sealed mode or requires local mirror resolution.
+
+## Handoff
+Use this doc as the PREP artefact for PREP-SCHED-SURFACE-01; update once datasets and sealed-mode rule are agreed.