feat: register every augmentation

[Hendrik-code]

Stacked on #67.

Each of the 51 augmentation classes now carries an @register(...) decorator naming its backend, its GEO/GE/TA group, and the backend-neutral concept it implements. smauglab/transforms/__init__.py imports them all, so importing that package is what populates the registry — that's what registry.load_all() does.

The batchgeneratorsv2 transforms the CPU pipeline composes are third-party and can't be decorated, so smauglab/transforms/cpu/external.py builds their entries by hand. Two things are declared per entry rather than assumed:

• wrap_random=False for transforms appended directly rather than inside a RandomTransform — they own no application probability, so a config setting p on them is an error.
• context_params for values nnU-Net supplies at runtime (patch size, rotation range) — a config must not set those.

The registered set and PIPELINE_ORDER now agree exactly: 29 GPU, 22 CPU — checked in both directions. Registration rejects a class missing from the table; a test rejects a table entry that nothing registers.

The if ladders still run and still decide what a config builds. Nothing reads the registry yet except the tests. That's deliberate: this PR is only about the metadata being present and correct.

Two things that had to come along

RandomDomainTransferGPU still took **kwargs, so registering it failed the no-**kwargs-without-forwards_to rule. Removed.

⚠️ #66's commit message claimed "**kwargs is gone from every transform constructor". That was true of every file it touched, but it did not touch domain_transfer.py — I'd reverted that file there to keep the PR focused. I've corrected #66's description.

Its bank path was a hardcoded absolute path into one machine's NAS home directory:

DEFAULT_BANK_PATH = "/DATA/NAS/ongoing_projects/.../domain_transfer_bank.npz"

That is exactly what the registry's external_asset field exists to describe, so it becomes the SMAUGLAB_DOMAIN_BANK environment variable — no baked-in default, and an error message that names the fix. Tests consult the registry entry rather than hardcoding the class name, so a second such transform is covered automatically.

Verification

With SMAUGLAB_DOMAIN_BANK pointing at the bank, all 24 seeded config digests are unchanged, including the domain-transfer one. Without it, that single config skips instead of running — the only behaviour difference, and the point of the change: it previously resolved by accident on exactly one machine and was silently broken for everyone else.

Full suite: 141 passed, 5 skipped, 478 subtests (up from 237 — every registered augmentation now gets a construct-and-run smoke test). ruff and mypy clean.

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