[HDX-12246] migrate: support customer-required clusters (6.4)

[barottomartin]

What

Retrofits the global hdxcli migrate command for turbine-api 6.4's multi-org breaking changes.

Since turbine-api 6.3 (HDX-11681), project creation requires an existing Customer on the target cluster, and tables may only reference storages/credentials that are members of the project's customer (HDX-11643). migrate previously forwarded the source project body verbatim (carrying the source cluster's customer UUID), which fails against 6.4 targets — exactly the break flagged on the ticket.

Changes

• New migrate/customer.py
  • Detects whether the target requires a customer from the projects OPTIONS metadata, so pre-6.3 targets are untouched (no version checks).
  • Resolves the target customer from --target-customer (name or UUID) → an existing target project's immutable customer → an interactive picker; offers to create the customer when missing, mapping 401/403 to an actionable insufficient-permissions message.
  • Registers the migrated table's non-default storages and autoingest credentials with the customer (add_storage/add_credential), always behind a confirmation, running before any resource is created so a decline or 403 never leaves a half-migrated project.
• resources.py — strip the source customer/org, inject the resolved customer on project create, run the membership pre-flight.
• commands.py — add --target-customer / -tc and document it.
• Bumps hdxcli to 1.0.84.

Scope

Per the ticket comment, this covers only the global migrate command. The config-only project migrate (and the shared migrate_resource_config engine) have the same break and are left as a follow-up; hdxcli project create is also affected and out of scope here.

Testing

• 21 unit tests in tests/test_migrate_customer.py (resolution precedence, OPTIONS gating, collectors, default-candidate rule). Full suite green.
• Live, cross-version:
  • 6.4 AIO (v6.3.0-rc.1-193): flag resolution, interactive picker, customer creation offer, existing-project inheritance, conflicting-flag warning, and the storage-membership pre-flight (decline aborts before any creation; accept runs add_storage and the table create passes validation).
  • Local docker on turbine v6.0.17 (genuine pre-customer release): old→new upgrade (v6.0 source → 6.4 target, customer resolved + injected) and the new→old regression guard (6.4 source → v6.0 target: "Target customer → Not required", all customer/membership logic skipped, project created as legacy).

Notes

• v1 nested URLs still work on 6.4 (no redirects/deprecation), so no URL changes were needed.
• No PyPI publish is triggered by merge (repo has no publish workflow); the version bump is unspent until a manual tag + upload.

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