Fix Monolith and Cobalt Stripe closing-block squeeze; guard Monolith flow notes

When only the closing block moved to page 2, the page-1 deficit was shared across every gap, including the closing block's own gaps, which cannot help page 1. Page 1 then came out a few points short and the totals spilled over with the closing block. Monolith and Cobalt Stripe now squeeze only the page-1 gaps in that case, as Marble and Highlighter already do.

Monolith's flow notes block could start in the last few points of a page and be cut into zero-height lines. It now holds 70 pt of room under its label first, as Marble does.

Adds tests for both cases (they failed before the fix) and notes in the template specs. Fingerprint goldens and thumbnails are unchanged.

docs/templates/03-monolith.md

@@ -156,3 +156,5 @@ Built as `src/pdf/templates/monolith/`: a standalone template (`tokens.ts` the t
 - **Elastic gaps.** The 88 pt band under the client (down to 24), the row padding (down to 6), the gaps above BILLED TO and under the client block (down to 14) and the two gaps in the footer (down to 8) give back Letter's missing 50 pt, and the overflow of an invoice that is a little too long for one page. A 2-item tax invoice with a bank block fits one A4 page that way; with 3 rows and a signature image the closing block moves to page 2 (the items and totals stay together on page 1).
 - **Amount in words and reverse charge** are the totals' left column (Medium 10.5, x 35..329). **Notes** and the **signature** (an image up to 150 x 45, or the signatory name and designation and the computer-generated line) form the band above the footer's top rule; notes taller than 110 pt flow as their own block before the closing.
 - **Footer position.** The closing block ends 24 pt above the "Generated with Voiced" line, so its bottom rule is at y 804 where Canva's is at 812.
+- **Closing moves alone.** When the items and totals fit page 1 only with the gaps squeezed and the closing block moves to page 2, the squeeze is computed from the gaps that help page 1 (band, info gaps, row padding) alone, as in Marble: the footer's own two gaps stay nominal and no longer take a share of the deficit. Before, the share was spread over all gaps including the closing block's, so page 1 came out a few points short and the totals spilled to page 2 as well (A4 with 4 or 5 rows, Letter with 4).
+- **Flow notes guard.** The flow-notes block is preceded by a zero-height `TableGuard` asking for 84 pt (14 gap + 70 hold), so it never starts with less than its label and first line of room and collapses into zero-height lines at a page foot; it starts on the next page instead (Marble's guard).