Fix #203 — %%scale and %%pagescale, as abcm2ps implements them

[sbeitzel]

Fix #203

Summary

• %%scale S and %%pagescale F (≡ %%scale 0.75 × F) are implemented with abcm2ps's behaviour and generation scope: file → following tunes, tune → that tune, last value wins. A body directive scales the whole tune and gets an info note (scaleAppliesToWholeTune).
• Baseline matches abcm2ps: with no directive a document renders at %%scale 0.75 (staff space 4.5 pt instead of 6).
• Everything the tune draws scales — music, chord/annotation/lyric text, title block, W: words. The page, margins and %%footer do not.
• Default font sizes are now abcm2ps's (title 20, subtitle 16, composer 14, info 14, tempo 15, gchord 12, annotation 12, vocal 13, words 16), in its nominal units, scaled with the page. Faces stay Libertinus Serif.
• SVGRenderConfig.scale (default 0.75) is the host default, like abcm2ps's -s; scaledStaffSize is the staff space as drawn.
• %%ceolkit:scale F ≡ %%pagescale F, with a deprecatedDirective warning (decision B).
• ckprobe --scale / --sweep set %%scale.
• Docs: EXTENSIONS.md, CONFORMANCE.md (§11.4.3, font table), README.md, CLAUDE.md.

Checked against abcm2ps 8.14

• §14.4 Canzonetta at its own %%scale 0.7 now prints on one page with a 22.4 pt title, as abcm2ps does (new tests).
• tunebook.abc paginates to 15 pages, the same count as abcm2ps (was 16). The Parting Glass now fits under The Radar Racketeer on page 3; abcm2ps starts it on page 4.
• Snapshots (Canzonetta, Zocharti Loch, simple jig ×2) re-recorded after a side-by-side visual comparison.

Test changes

Geometry tests that used SVGRenderConfig().staffSize as the drawn staff space now use scaledStaffSize; a few tolerances moved from 1e-6/1e-9 to 1e-3 for rounded SVG coordinates; three tests got more music so they still overflow a line or page. Tests that used %%ceolkit:scale as a tool now use %%pagescale.

Upgrading

• Output is now 75% of its previous size by default, matching abcm2ps's %%scale 0.75. More fits on a line and a page, so line and page breaks move. For the old size, add %%scale 1 (≡ %%pagescale 1.333) or set SVGRenderConfig.scale = 1.
• Default text sizes are now abcm2ps's, and every text except the footer scales with the page.
• %%ceolkit:scale F is deprecated and now means %%pagescale F: it scales the title block and words too, and the same value prints at 75% of its former size.

Test plan

• swift build
• swift test — all suites pass
• Canzonetta compared visually with abcm2ps output

🤖 Generated with Claude Code