feat(07-04): the budget-audit CLI + the root npm script — orchestration, free-tier comparison table, 0/1/2 exit codes

- npm run budget-audit: 5 required gates + the --live cache-header probe; one evidence line per gate
- the FREE-TIER COMPARISON table: every documented Cloudflare free-plan ceiling beside the
  current value where measured, `not measured` where not — the console form of docs/BUDGETS.md
- exit 0 CLEAN / 1 FAILED / 2 NOT RUN — a skip is never a pass (T-07-22)
- no secret, no coordinate in the output (D-14's category-only law, applied to budgets)

package.json

@@ -17,6 +17,7 @@
     "gallery": "npm run gallery --workspace theme",
     "audit": "npm run audit --workspace theme",
     "privacy-audit": "node scripts/privacy-audit.mjs",
+    "budget-audit": "node scripts/budget-audit.mjs",
     "capture": "npm run capture --workspace theme",
     "bot:test": "npm test -w bot",
     "bot:typecheck": "npm run typecheck -w bot",