Rewrite CLAUDE.md with a commands + architecture…

Details

Adds the standard header, a Commands section (the order-dependent offline
build sequence, css:check vs local-only lint:css, changelog/versioning,
db:* scripts, the TPP/EDCR golden test suites) and an Architecture
section: the coexisting v1/v2/v3 Jekyll versions and their
layout/includes/sass/css/TS mapping; the global-script TS model (no ES
modules, shared window, load-order-as-dependency-graph); runtime Supabase
content via db:// + section_items; the generated runtime config; the
canvas backgrounds + EDCR/TPP explainer pipelines; and the CI/deploy
topology.
Corrects two stale points: the "v2 theme" framing (v3 is the flagship at
/) and the offline build order (tsc must run after jekyll, which wipes
_site). Preserves the existing validation-matrix, offline-validation,
section-seeding, and git-convention sections.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01S2zE1oUnd7vE9VYymfS2Ab

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