fix(cli): connector dash gate honours pathLength

[miga-heygen]

Follow-up to #3912 (stacks on fix/connector-detached-dash-hidden; merge that first).

Summary

• shaftDashHidden now honours the SVG pathLength attribute: the dash window is judged in the author's units (path.pathLength.baseVal, a plain number that is 0 when unset) instead of always against getTotalLength(). dashLength / dashArrayLengths remain the single owners of parsing and units.
• The total > period shortcut is gone so the ≤10% rule applies uniformly — a window that spans a whole period without enclosing a whole dash (2 97 on a 100-long path at offset 0.5 paints 3%) is hidden like any other sub-10% stroke; patterns that do enclose a whole dash are still caught by the in-loop check.
• A present pathLength that resolves to 0 (pathLength="0", or an unparseable value such as abc) zeroes Chromium's dash scale factor and the stroke paints solid, so the gate returns painted instead of falling back to the real length and judging the window inside a gap (which suppressed a real connector_detached). A negative pathLength is ignored by the browser and keeps the existing fallback.
• The dash-offset wrap adds the period only to negative remainders; ((offset % period) + period) % period is off by one ulp for fractional offsets (0.9 % 2 → 0.8999…), which flipped the exact 10% boundary in pathLength units.

Why

<path pathLength="1"> with stroke-dasharray: 1; stroke-dashoffset: 1 is the canonical CSS draw-on idiom and renders zero ink, but the gate compared the dashes (author units) against the real user-unit length, so the period looked tiny next to the path and connector_detached still fired on a shaft that had not started drawing.

Test plan

• layout-audit.browser.test.ts dash table: +7 rows — pathLength=1 with 1/1 (hidden), 1/0.9 (10% boundary, hidden), 1/0.5 (painted), 0.1 0.9 round dot (painted); 100 at offset -150 (painted; only the wrap gets it right); 10% / 10% (hidden; percentages resolve against the 1740×830 viewport, not as bare numbers); 2 97 at 0.5 (hidden, no full-period shortcut); pathLength=0 with 100/100 (painted: a zero pathLength renders solid). installConnectorGeometry mirrors the DOM's pathLength for happy-dom, parsing it as an SVG number (anything else, including Infinity and hex, reads as 0).
• Each new row was mutation-checked: ignoring pathLength, dropping the negative wrap, parsing % as bare numbers, restoring the full-period shortcut, restoring the double-modulo wrap, or dropping the zero-pathLength guard — every mutation kills at least one row.
• Suite: 143 pass under vitest run src/commands/layout-audit.browser.test.ts (node runner, sibling packages built first as in CI).
• Real Chromium (rasterised, 6px stroke on a 360-unit path): pathLength=1 1/1 → 0 inked px; 1/0.5 → 1080 (50%); 0.1 0.9 round → 248; 1/0.9 → 216 (exactly 10%); 2 97 at 0.5 with pathLength=100 → 60 (2.8%); solid control 2160; pathLength=0 and pathLength=abc with 100/100 → 100% ink (solid), where the previous gate reported hidden. path.pathLength is an SVGAnimatedNumber whose baseVal is the number itself (1 when set, 0 when unset).
• tsc --noEmit -p packages/cli, oxlint, oxfmt --check clean on the changed files.

🤖 Generated with Claude Code

[miga-heygen]

Addressed in e61ec8d.