feat(storage): Phase 6 adapter foundation for Postgres and Azure Blob

[Yuge Zhang (ultmaster)]

Implements the Phase 6 storage foundation: shared SQLite/Postgres codecs, validation, identity allocation, and Task/Run rules; native Postgres structured repositories; Azure Blob storage; and async agent extension-document helpers. Each SQL backend retains its own migrations, queries, and transactions.

This is 1 of 2 stacked PRs. The application continues to select its existing Disk/SQLite profiles. The second PR, #185, migrates Agenetes persistence, enables all six backend pairings, and adds conversation/product coverage. Review and merge this foundation first; then retarget/rebase #185 onto main before merging it.

Includes its own pnpm test:storage-backends command and CI step using disposable PostgreSQL and Azurite containers. Coverage includes real transaction rollback, CAS across independent connections, Workspace isolation, restart, staged-upload failure, and same-key upload serialization. Azure uploads publish only after successful block commit.

Validation of this foundation independently:

• pnpm run typecheck passed.
• pnpm -r --if-present --no-bail run test passed, including 1,401 server tests.
• pnpm test:storage-backends: 121 checks passed.
• Lint passed with no errors; formatting passed. Existing skips/todos remain unchanged.

The upper PR uses an identical mirror of this head branch in microsoft/Huabu as its base so its diff contains only activation work. Both PR heads remain on the fork. Azure validation uses Azurite; multi-Server coordination and live-account validation remain outside this change.