feat(viz): bring the memory web assets onto the published brand

[bkearns]

viz.html and workbench.html had drifted into a look of their own. They now use the same tokens as the site (ferrosa-docs docs/site.css), so the product and the marketing surface read as one system.

The monogram was an invented product element

Both assets rendered Fm with atomic number 100 — Fermium, invented for "Ferrosa Memory" — in the header mark and the favicon. The brand rules forbid this twice:

The Fe monogram is locked to the company mark only. Products do not get element tiles of their own.
Don't: swap element symbol or atomic number for products.

Both now carry the company Fe / 26 mark with the brand gradient ending in Blued Steel, matching logo.svg.

Tokens

Names now match the site: --primary is Core Blue and --accent is Electric Cyan. The assets had --accent holding Core Blue and --accent-warm holding cyan. Invented tokens --accent-cool and --accent-purple are retired onto --primary and --steel. Blued Steel, Pale Cyan and the border/hairline scale were missing entirely.

The graph palette extends the brand rather than inventing beside it

31 ad-hoc hues encoded entity and edge types — hot pink #ff7eb3, coral #ff6b6b, violet #c97eff, sky #87ceeb, and 20 more with no relationship to the brand. They are replaced by a categorical ramp built from the cool family (Electric Cyan → Core Blue → Blued Steel), with the semantic colours reserved for meaning rather than spent on categories.

Edges sit closer to steel than nodes do, so relationships recede behind the entities they connect instead of competing with them — which is also what brand guidance means by keeping Blued Steel to fills and strokes.

Colours resolve from CSS tokens at render time instead of being duplicated in JS, so the graph follows the theme rather than painting dark-ground hues onto a light ground.

Light theme

Neither asset had one. Both now support an explicit data-theme and the host's preference. Light values are darkened counterparts, not the dark values reused — a hue picked for #05070c does not survive on #f4f8fd, which is why the site darkens --accent to #0e7ea3 rather than reusing it.

Composite values became tokens for the reason the site documents: an rgba() or gradient literal cannot flip, because its alpha sits over a different ground in each theme. That covers chrome gradients, menus, inputs, films and shadows — including shadows that were pure black, which the brand says never to use, and several neutral greys that were not brand colours at all.

Other conformance

• Focus ring is 3px Electric Cyan with an offset, not a 1px hairline
• All 41 border-radius declarations sit on the 4/8/12/16 scale (6px alone appeared 11 times)
• Pure-white selection rings and on-accent text became --text / --on-primary, which flip

Guard

scripts/check-viz-theme.py fails on three things: the two light blocks drifting, a dark token with no light counterpart, and a colour literal painted in a rule.

The first is not hypothetical — while writing this, --film was added to the explicit block and the prefers-color-scheme copy silently kept the old palette. That is invisible until someone views the page on a light-preference host with no saved choice. CSS cannot alias one block from the other, so the guard is the only thing keeping them honest. Wired into make test-unit.

The workbench branding test asserted the old state, including the Fm mark. It now asserts the brand contract and the absence of the invented tile.

Verification

Both assets rendered in both themes via headless Chrome, and exercised against a real 14,404-node / 54,510-edge graph — see ferrosadb/ferrosa-docs#25, which reshoots the homepage image from this build.

109 http tests pass; ferrosa-memory-core builds; check-viz-theme clean; cargo fmt --check clean.

Not merging this myself: standing rule is no auto-merge on public repos.