Summary

Closes #2503.

• Adds pnpm lint:ui:no-css-class-drift script invoking the existing scripts/audit-css-class-drift.mjs (landed in audit(ui): CSS class drift audit script (#2502) #2507 / audit(ui): one-shot CSS class drift audit — surface fork-side references with no CSS definition #2502).
• Appends the new script to the pnpm check chain — the lint CI job already runs pnpm check, so the drift gate now runs in CI automatically without any workflow edit.
• Documents the gate in CLAUDE.md in two places: § Formatting & Linting (local-dev orientation) and § Fork-integrity gates (CI / fork-lifecycle orientation, alongside the existing rebrand / zombie-import / stub-debt / throwing-stub-callers / obsolescence-audit gates).

Baseline verification (AC: "All findings from D-1 resolved BEFORE wiring")

On main at branch base (20984fb998):

CSS class drift audit
  CSS files (import graph): 14
  TS/TSX files scanned:     118
  Classes defined:          733
  Classes referenced:       403
  Orphans:                  0

All drift clusters identified by #2502's audit were resolved in merged PRs #2506 (→ #2501), #2512 (→ #2510), #2513 (→ #2508), #2514 (→ #2509), and #2515 (→ #2511). Wiring this gate now will NOT make CI permanently red.

Gate behavior verification

Full pnpm check run on this branch: passes (format:check, tsgo, oxlint, lint:tmp:no-random-messaging, lint:no-remoteclaw-ai, lint:ui:no-css-class-drift).

Adversarial test: injected a fake class definitely-not-a-real-class-xyz-probe into ui/src/main.ts →

Orphans: 1
ELIFECYCLE Command failed with exit code 1.

Post-revert: Orphans: 0, exit 0. Gate catches drift; pnpm check fails on any class reference with no matching rule.

Script naming deviation

Issue #2503 AC line 6 suggests pnpm lint:css-classes. Project convention is lint:<area>:<predicate>, established by:

• lint:ui:no-raw-window-open
• lint:tmp:no-random-messaging
• lint:plugins:no-monolithic-plugin-sdk-entry-imports

Used lint:ui:no-css-class-drift to match — ui area scope (the check scans ui/src/**/*.{ts,tsx,html} and ui/src/styles.css import graph), no-<thing> negated-predicate form. The issue's lint:css-classes was a proposed name in an "Implementation plan" section; the AC is about the check running in pnpm check, which this PR delivers.

AC coverage

Test plan

• pnpm install (worktree was fresh; dependencies installed)
• node scripts/audit-css-class-drift.mjs baseline: 0 orphans, exit 0
• pnpm check full chain passes locally (~15s total)
• pnpm lint:ui:no-css-class-drift runs in isolation: exit 0
• Adversarial test: fake orphan injection → audit reports 1 orphan, pnpm exits 1
• CLAUDE.md renders correctly (markdown preview)
• CI lint job passes on PR

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