feat(templates): add the SerifHeadline two-column CV preset

[DemchaAV]

Why

The third CV bundle in the queue is the one that stops being a sidebar. It is a two-column editorial sheet with a serif masthead, a timeline of roles beside grouped skill meters, and two full-width bands of marked cards closing it — 235 laid-out nodes against the 87 and 158 of its predecessors.

It is also the one whose geometry is not a set of numbers somebody typed. The design was drawn on a 1024-pixel grid and every distance in it is that grid put through a scale, with each vertical gap expressed as the ink the drawing shows rather than the margin a line box needs. Porting it meant porting that arithmetic, not its results.

What changed

• cv/presets/SerifHeadline — a DocumentTemplate<CvDocument> via create(), split for the 500-LOC rule into package-private SerifHeadlineStyles (the grid, the type metrics and the gap arithmetic), SerifHeadlineWidgets (the heading, the plate, the N-column band), SerifHeadlineMasthead, SerifHeadlineMain, SerifHeadlineAside, SerifHeadlineClosing, SerifHeadlineText and SerifHeadlineIcons.
• The arithmetic came across, not its output. gap(inkPx, blankAbove, blankBelow) states a distance as the white between letters and subtracts what the two line boxes already contribute; heights carry a compression factor on top of the width scale, because the drawing is proportionally taller than A4. Freezing the results as literals would have been unmaintainable the first time a type size moved.
• The three closing bands are a layer stack, not a row: the marks hang outside their columns and the separators sit exactly on the column edges, both of which a row's slots would clip or push. Every child is placed by computed insets instead.
• The trailing rule on a full-width heading is authored, so its width comes from an estimate of what the tracked capitals will measure — three advance classes and a 3% margin that errs short. The engine offers no measurement at compose time, and the estimate is documented as one.
• Eight berths reach their sections by title. Soft skills are matched before skills, because "Soft Skills" names both and the block with a shape of its own should win it — pinned by a test.
• Projects and achievements take the mark each entry names in CvEntry.icon(); the vocabulary is this preset's own and an unknown token is reported as a data error listing the set. The certification medal is chrome, not data. The employer's city and the campus come from CvEntry.place().
• The eleven marks ship inside the templates artifact under templates/cv/serif-headline/icons/.

Verification

Full reactor gate (the eight CI modules) → BUILD SUCCESS; the CV preset suites 30/30; examples suite 77/77 including CommittedAssetDriftTest with the new preview; javadoc:javadoc → BUILD SUCCESS with no warning naming a new file.

Port parity, verified against the published template itself: the preset fed the template's own fixture is pixel-identical to the standalone render — 0 / 2,173,720 differing pixels, and the layout snapshot matches node for node — 235 of 235, same names, zero geometry delta. The bundle's geometry is the same on its pinned 2.2.0 and on this branch (235/235 nodes, zero deltas > 0.01pt); the two engines differ only by the released ligature fix (#601), so the current-engine render is the parity target.

Notes

• The sheet holds one page. The body is a single row, and a row is atomic, so a CV longer than the sheet raises AtomicNodeTooLargeException rather than flowing or dropping entries — the same contract the two sidebar presets landed with, documented on the class, in using-templates.md, and pinned by a test.
• A certification title wraps inside its narrow column, which is the design rather than a defect: the reference does it too, and the smoke test asserts either side of the break rather than across it.
• trackedWidth is an estimate, so a heading long enough to make its trailing rule overlap the letters would not go red. The margin errs short and the snapshot freezes the fixture's rules; the method says as much.

Lane: canonical (templates.cv.presets + qa + examples) — no engine changes, no model changes (those landed in #618).