v1.3.0 — cinematic comet tail (009)

Cinematic comet tail (PR #12)

The 4 staggered ghost-circle trail is replaced with a single rotating
gradient-ellipse tail. The tail now has a visible taper, glows softly,
and always orients along the comet's direction of travel.

What changed

• Gradient-ellipse tail: one <ellipse> (rx=56, ry=3) with a 5-stop
  <linearGradient> and <feGaussianBlur> softening. <animateMotion rotate="auto"> aligns the gradient's head-to-tail direction with the
  path tangent, so the tail always trails the comet correctly.
• Head shrink: nucleus −15% (2.2→1.85), semi-transparent coma halos
  −30% on top of that (inner 5.5→3.29, outer 9→5.36). The head now
  reads in scale with the surrounding stars instead of overwhelming them.
• Bundle: ~1 KB smaller per animated SVG — one ellipse replaces four
  ghost circles with their animation elements.

Why

The Vercel prototype's JS comet (https://comet-contribution-graph.vercel.app)
has a visibly tapered, glowing tail that reads as a direction of travel;
the shipped 4-ghost stagger read as an undirected ~15-20 px smear. The
prototype's exact technique (per-frame getPointAtLength + dynamic gradient
endpoint repositioning) is not portable to SMIL, so the closest SMIL-native
analogue is a rotating gradient ellipse — see
spec
and designer feasibility memo.

Validated against 4 benchmark accounts

a, b, c, d — 6-way variant comparison in
a local scratch folder (gitignored), winner chosen visually.

Compatibility

Drop-in replacement. Action consumers on @v1 pick up v1.3.0 on their
next bootstrap run. No config changes, no new inputs.