fix(rest/nodejs): bump @ucp-js/sdk to 0.4.5 so quantity bounds hold at the schema boundary

[vishkaty]

What

The pinned @ucp-js/sdk 0.4.3 generates LineItemCreateRequestSchema and LineItemUpdateRequestSchema with quantity as a bare z.number(), so a create or update carrying quantity 0, a negative quantity, or a fractional quantity crosses validation and is priced; a negative quantity produces negative checkout totals (#194).

Fix

Bump to 0.4.5, which restores the line_item.json contract, integer with minimum 1, at both request schemas (js-sdk#53). One code touch rides along: 0.4.5 types date-time fields as strings, so the single Date valued assignment, the shipped event occurred_at, moves to toISOString, same wire bytes, sound types.

Testing

• New test/quantity_bounds.test.ts pins the boundary: 0, -1 and 1.5 draw 422 on create, -1 draws 422 on update, and a positive integer still prices normally, total 7000 for quantity 2 at 3500. All three rejection tests fail on 0.4.3 and pass on 0.4.5.
• Full suite 158 passing on the bump; tsc and the pinned pre-commit are clean.
• The Python reference already rejects these bodies at its schema boundary, so both lanes now agree.

Fixes #194.