[codex] Update primary brand color

[Rabithua]

Summary

• Replace the Rote primary brand color with #3ECF4A across theme tokens, logo assets, heatmap, export cards, and login/home/filter surfaces.
• Split the landing page into focused section components so the touched source stays within the project quality gate.

Validation

• git diff --check
• cd web && bun run lint
• cd web && bun run build
• Browser smoke: /setup renders with --color-theme #3ECF4A; retry button responds; mobile viewport checked.

Notes

• Local browser smoke redirected to /setup because the local backend was not running.

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