fix(performance): stabilize browser budget measurements

[furedea]

Summary

• self-host the Japanese web font to remove render-blocking third-party font requests
• collect three measurements normally and two confirmation measurements after a variable-metric breach
• retain all samples and report medians, ranges, sample counts, and recovered instability
• reuse the Playwright browser with a fresh context for every sample
• supersede ADR-0011 with the stabilized measurement decision

Verification

• pnpm run test
• pnpm run typecheck
• pnpm run lint
• pnpm run format:check
• pnpm run knip
• build, end-to-end, and performance checks run in CI

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