Replace raw blob/tree ports with git-cas asset and bundle handles

[flyingrobots]

Parent: #734
Blocked by: #735

Outcome

WARP services exchange opaque git-cas handles and retention results, never naked storage OIDs or hand-assembled Git trees.

Scope

• Remove BlobStoragePort and CasBlobAdapter sequencing.
• Remove writeBlob/readBlob/writeTree/readTree from domain-facing persistence ports.
• Migrate patch content, patch journal, strand patches, wormholes, query content, discovery, writer, audit, trust, and strand descriptor payloads.
• Replace CasPayloadPointer and raw pointer blobs.
• Keep WARP causal commit/ref rules behind semantic operations.
• Return staged storage evidence and attach retention witnesses to WARP receipts.

Proof

• Streaming content round trips without full buffering.
• Causal commits retain every referenced asset.
• Domain import gate has no raw Git object-write capability.
• Existing Remove per-artifact ports + defaultCodec #528, runtimeHelpers imports infrastructure adapters and branches on plumbing presence #174, and WarpRuntime.open constructs infrastructure adapters by peeking at plumbing #182 are closed or narrowed with source evidence.

[coderabbitai]

🔗 Related PRs

#68 - fix: throw on missing content blob oids [merged]
#72 - feat!: mandatory CAS blob storage with streaming I/O (OG-014) [merged]
#93 - Fix recursive tree OID read fanout and release v17.0.1 [merged]
#107 - Prepare v18.0.0 release metadata and final gates [merged]
#726 - Move graph exports behind v19 public API boundary [merged]

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[flyingrobots]

Dependency #735 is closed via merged PR #744 (a7976ade6d036316a28844a977743dc45e1196b6). Activating this slice on top of merged #746; implementation inventory is in progress.