fix: registration fence for script-defined tasks under Python 3.14

[dcx]

Fix: registration fence for script-defined tasks under Python 3.14

ws.tasks.register(fn) for a bodyless task defined in a run-as-script file (__main__) captures the function's definition as its artifact. If the signature annotates with a name only the script defines — a local class, or any non-shepherd import — that name won't travel with the artifact, so registration is supposed to refuse early with a "move it to an importable module" message.

That check relied on the def statement evaluating its annotations eagerly, which two things defeat:

• Python 3.14 (PEP 649 / PEP 749) defers annotation evaluation by default, so the def no longer raises for an unresolved name and the check silently passed — surfacing the failure later, more confusingly, instead of at registration.
• A string forward-reference annotation (thing: "LocalThing") is never evaluated by the def on any Python version, so it slipped through everywhere.

The fix

Force annotation evaluation explicitly (get_type_hints against the generated artifact's own globals, which carry only import shepherd as sp) instead of relying on the def to do it. An undefined name now raises NameError — and the teachable refusal — on every supported Python (3.11–3.14). No change for valid tasks: normal May[GitRepo, ...] / str / None annotations resolve cleanly.

Tests

Adds a string-forward-ref regression test that fails against the old check on every Python (not just 3.14), so the behavior is guarded on the interpreters CI already runs. Verified: the registration ergonomics suites pass on both 3.12 and 3.14.

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