Test register families with fixed-seed properties

[christian-byrne]

Adds reproducible fast-check properties for node presence/incarnation, widget, concrete input, promoted input, and inputcount registers. Each family runs 240 fixed-seed scenarios covering version, actor, and op_id tiebreaks; winner and loser retries; three batch/interleaving shapes; and both arrival orders. Post-run vacuity guards require every dimension to have nonzero sampled coverage.

This holds KA-2 embedded total ordering, KA-4 convergence/idempotency, and KA-10 single-snapshot forks. The inputcount assertion is deliberately register-scoped: it sorts source output link references before cross-order comparison because those references remain arrival-ordered outside this PR's register-family scope.

Verification:

• Node 25.9: build, purity, pins, profile claims, CodeRabbit generation, statelessness, corpus, typecheck, and focused property suite pass; full Vitest is 819/827 with the eight known dependency-cruiser Node 25 incompatibility failures.
• Node 24.20: import graph passes (17 modules / 46 dependencies) and full Vitest passes 827/827.

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• test/register-families.property.test.ts

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