TITLE: PHYLLOTAXIS — one angle, two hundred and thirty-three

PROMPT:
Create a self-contained HTML page (all CSS and JS inline, no external fonts, images, CDNs, libraries or external SVG files) called "PHYLLOTAXIS — one angle, two hundred and thirty-three". Art direction: botanical, dark green-black with seed gold. Palette: ground #0c100b, ink #e9eee2, dim #7d8a74, hairline rgba(233,238,226,.13), seed #e8c25a, leaf #7fae4e. Layout: a header with a two-dot logo and a monospaced formula line; then a hero with a seed kicker, a huge light-weight headline with one bold word, and a paragraph; then a bordered stage holding a 1000×1000 canvas that draws the seed head as a spiral of discs whose size and colour change with radius, plus an absolutely positioned monospace HUD; then a control band of two sliders (Divergence angle, Seeds) and four buttons (Golden angle / 90° square grid / Fibonacci overlay / Grow); then a six-item readout strip giving the angle, the angle as a fraction of a turn, the nearest consecutive Fibonacci pair, the number of spokes in each direction, the number of visible seeds and the packing density; then a two-column section pairing an essay on why 137.5 degrees is the only good answer with a note on the counting; and a footer. The head is generated by the real construction: the nth seed sits at a radius of c times the square root of n and at an angle of n times the divergence angle, which gives an even packing rather than a spiral of overlapping lines. Interaction: the angle slider moves the divergence angle away from and back to the golden angle, and at 90 degrees the head visibly collapses into a square grid while at 120 degrees it forms three rigid spokes; the Seeds slider changes the count; Fibonacci overlay draws the individual spiral families that are visible in the head; Grow animates the head filling up seed by seed. Responsive: the two-column section stacks under 860px.

DESCRIPTION:
A seed head generated by the real construction: the nth seed at a radius of c√n and an angle of n times the divergence angle. Drag the angle away from 137.5 degrees and the head develops scars — at 90 degrees it collapses into a square grid, at 120 degrees into three rigid spokes — and the Fibonacci overlay draws the individual spiral families that you can count in a real sunflower.

MAJOR VISUAL TECHNIQUES:
- Phyllotaxis construction with radius proportional to the square root of the index
- Seeds coloured and sized by their radius so the head reads as a gradient
- Fibonacci spiral families traced through the point set
- Nearest consecutive Fibonacci pair computed from the seed count
- Angle expressed as a fraction of a full turn
- Grow animation that reveals the seeds in order

INTENDED INTERACTION MODEL:
Turn the head. Move the divergence angle and watch the packing fail, restore the golden angle, overlay the Fibonacci spirals, and grow the head from the centre out.