Build against chobble-template main; compact, corporate theme refresh

[stefan-burke]

Summary

Makes the design more compact and professional, and removes the stale pinned chobble-template submodule so the site builds against chobble-template main from GitHub.

While wiring up the build, the content turned out to be incompatible with both the pinned submodule (too old) and main (renamed layout, changed hero schema). This PR migrates the content to the current main schema so the site builds, then applies the visual refresh.

Build / template changes

• Remove the pinned chobble-template git submodule and build against chobble-template main from GitHub (the build scripts already clone it; the submodule was only providing the @chobble/js-toolkit dev dependency).
• Migrate page content to the current template schema: drop the renamed design-system-base.html layout so pages use main's default base.html, and convert the hero blocks from name/lead to the current content field (not-found.md, thank-you.md).
• Exclude VOICE.md from the published site — main now applies a default layout to everything under src/, so the docs file was being rendered as a page.
• Drop the @chobble/js-toolkit dependency (only sourced from the removed submodule) and reimplement scripts/precommit.js to orchestrate lint/cpd/build without it.

Design changes (css/theme.scss)

• Compact vertical rhythm: pull --space-3xl in, which feeds every --section-padding-y-* variable — roughly 12% shorter homepage while staying readable.
• Sharper corners (--border-radius 6px → 4px) for a more corporate feel.
• Crisp white nav bar with a brand-red top accent and soft shadow; tighten the menu so all nine items hold a single line instead of wrapping onto an awkward second row.
• Logo fills the bar: enlarge it and add a tightly-trimmed brand-mark.png (the source PNG had heavy baked-in whitespace, so it floated small in the nav).
• Corporate polish: brand-red uppercase "eyebrow" labels above split headings (e.g. "BS EN 14960:2019") and a thin brand rule atop each feature card.

Verification

Built cleanly against chobble-template main and screenshotted at mobile/tablet/desktop. Nav now sits on one line with a filled logo; migrated hero pages (thank-you / 404) render correctly; content pages unaffected.

Note: bun run lint currently fails on a pre-existing Biome version mismatch (CLI 2.5.0 vs config schema 2.3.11 + a removed noUnnecessaryConditions rule), unrelated to these changes.

https://claude.ai/code/session_01SGhcb3D7nyGY8P55V7zJsb

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