This PR migrates all tailwind configs in the apps to be CSS configs.
They import a shared CSS Tailwind config from the `config` package
(which in turns imports the old JS config).
The shared JS config will be migrated to CSS in a followup PR.
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## Summary by CodeRabbit
* **Chores**
* Centralized Tailwind into a config-driven entrypoint and updated the
app build flow to use the new build step; many apps now import unified
global styles.
* **Style**
* Migrated global styles to a Tailwind v4-style setup, added
project-wide content scanning, consolidated theme imports, standardized
theme tokens (including new --container-site max-width), and added a
small prose utility to remove paragraph margins.
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Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>
