feat: complete portable renderer correctness

[bitgorust]

What changed

• Add contained portable image/font assets and exact final-byte accounting.
• Add complete bounded authoring preflight before permission or writes.
• Add fixed-slot, contrast-checked design tokens.
• Add accessible and internationalized semantics, keyboard flows, RTL/locale/time-zone handling, reflow, motion, and print behavior.
• Add reproducible CLI/browser performance and byte budgets.
• Record the Fedora 44 / Orca 50.2 / Chrome 151.0.7922.137 manual screen-reader pass from Aaron Zeng.

Why

Goal 3 closes the Phase 2 correctness track so portable artifacts work offline with bounded resources and accessible real-surface behavior.

User impact

Generated pages can embed safe project assets, surface complete authoring errors before writes, use bounded project styling, remain usable across keyboard/mobile-width/RTL/screen-reader flows, and enforce measured performance budgets.

Validation

• npm test: 214 passed, zero failed or skipped.
• npm run build: pass on Node 24.
• npm run check: all 35 checks pass.
• npm pack --dry-run: 63 files, 116.5 kB packed.
• Real Chromium desktop/mobile-width/zoom/RTL/console/request evidence retained.
• Manual Orca checklist: pass.

Comparative quality, representative users, physical-mobile coverage, and broad support certification remain explicitly assigned to Goal 5.