feat: consume-tokens example + stdlib sitecheck CI

[Pattermesh]

What

Two additions to the brand kit, both vanilla / zero-framework:

1. A worked consumer example — examples/consume-tokens/

The canonical "drop tokens.css in and you're on-brand" reference. A small settlement-monitor app (header, metric cards, status table, button row, alert) built purely from the published var(--*) custom properties. It imports only tokens.css — no page.css, no component library — and every rule in its own thin stylesheet reaches for a token first. Linked from the root use section and added as a tile in the components dashboard (pages/index.html).

2. A static-site checker + CI — tools/sitecheck.py, .github/workflows/sitecheck.yml

A pure-stdlib Python checker (no dependencies) that walks every .html file and asserts:

• well-formed — markup parses, exactly one <!doctype>, every non-void element that opens also closes;
• links resolve — every relative href/src and in-page / cross-page #fragment points at something that exists on disk (external http/mailto/// links are out of scope);
• tokens wired — any page using var(--token) must <link> a stylesheet that resolves to tokens.css (directly or via a sibling sheet that pulls it in) — the one bug a design-system site must never ship.

The check functions return problem lists so they're unit-testable. tools/test_sitecheck.py has 27 pytest cases (good- and bad-case per check) plus a gate asserting the real tree is clean. The workflow runs the checker CLI then pytest on push/PR.

Tests

$ python3 tools/sitecheck.py
sitecheck: 16 file(s) OK — well-formed, links resolve, tokens wired

$ python3 -m pytest tools/test_sitecheck.py -q
27 passed

Verified the gate has teeth: deliberately breaking the example's tokens.css link makes sitecheck.py exit 1 with broken-link, unresolved-stylesheet, and tokens-not-wired errors.

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