Enforce Tailwind conventions in CI (class order + no arbitrary text sizes)

PR #2175 added the tooling to keep Tailwind tidy but nothing enforces it, so main keeps reintroducing arbitrary values (it happened on every rebase of that PR). Convergence is currently manual.

Proposal

Add a CI check (GitHub Actions) that fails when Tailwind conventions drift:

1. Class order — run ai/tw-sort --check --all (rustywind --check-formatted); non-zero exit if any file is unsorted.
2. No arbitrary font sizes — grep-gate for text-[…px/rem] in app/views / app/frontend / app/helpers; fail with a pointer to the text-2xs/3xs/4xs scale.

Notes

• The repo is not yet fully sorted (only touched files converge in #2175), so --check --all would fail today. Options: run the sorter repo-wide first (one big mechanical PR), or scope the check to changed files only until the tree is clean.
• Keep it fast — rustywind is a native binary; the grep is trivial.

Context: split out of #2175.

Review PR #2175 and the existing ai/tw-sort tooling first; inspect how GitHub Actions currently runs checks. Decide whether the check targets all files or changed files while the tree is unsorted, then verify the workflow rejects unsorted Tailwind classes and arbitrary text sizes under app/views, app/frontend, and app/helpers.