improve(make): lead with the looping GIF, prompt the first rectangle, humanize lab tooltips

[silviot]

First of the "quick wins" toward the three goals. Voice/copy changes — please redline before merge; nothing auto-merges or deploys.

What & why

Goal 1 — make the loop the hero (it was buried).

• Export and Share menus now lead with the Looping GIF (the shareable artifact), instead of burying it third under a misleading "Image".
• Reworded in plain language; the still-PNG item is renamed "Still image (PNG) — A single moment, not the loop." so nobody clicks it expecting the animation. Dropped the only jargon in the menu (480px · 25fps).

Goal 1 — cold-start guidance.

• A prompt now appears over the photo until the first rectangle is drawn: "Drag a rectangle on your photo — that's the part that spirals into itself." (Previously the only hint lived in the preview pane, so a first-timer with their own photo saw two dark panels and no instruction.)

Goals 2/3 — stop hiding the math behind notation.

• The two math-view rail tooltips go from Pipeline (log · rotated log · tententoon) / Complex playground (f(z) explorer) to plain language borrowed from your explain voice: "See how the spiral is built — log it, bend it, spiral it" and "Playground — bend any image with a complex function."

Scope notes

• No rendering/export logic changed — only menu order, copy, one overlay, and tooltips.
• Did not touch the .human-written InfoModal block (its "Read & watch" list is inside it). A standalone /explain link is deferred to the fold-into-one-app work, since that page is folding in anyway.
• Desktop copy-to-clipboard + a real success card + collapsing the duplicate Export/Share menus → PR-2. Carrying your voice into the in-panel lab labels (β = atan(logS/2π), etc.) → PR-3 (I'll bring the full string list first).

Gate

• npm run check — 0/0
• npm test — 44/44
• npm run build — clean

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