feat(statistics): add exact paired sign test

[drewstone]

Summary

• add an exact one-sided paired sign test for numeric task differences
• require an explicit greater/less direction, exclude ties, and expose every denominator
• reuse stable log-space binomial tails for McNemar without changing its result contract
• release as additive 0.114.0

Why

R358 hard-coded the all-positive value for three tasks after its comparison fell to two.
This makes the statistic reusable and prevents another consumer from repeating that error.

Verification

• pnpm typecheck
• pnpm test — 2,810 passed, 2 skipped
• pnpm build
• pnpm lint — exit 0 with four pre-existing warnings
• packed-package import and execution
• clean merge tree against current origin/main

Compatibility

Additive root export; no fleet-wide bump required.

[tangletools]

✅ Auto-approved drewstone PR — 009d1a1e

This PR was opened by the trusted drewstone account.
The full PR reviewer audit still runs separately and will publish findings if it detects issues.

_{tangletools · auto-approval · reason: drewstone_author · 2026-07-11T08:36:41Z}

[tangletools]

✅ Auto-approved drewstone PR — a0cf25fa

This PR was opened by the trusted drewstone account.
The full PR reviewer audit still runs separately and will publish findings if it detects issues.

_{tangletools · auto-approval · reason: drewstone_author · 2026-07-11T08:39:30Z}