Localize Mermaid render status copy

[jerryfan]

This keeps pi-mermaid English by default, but makes the render-status path optionally localizable.

Why these strings:

• parser unavailable, too-many-blocks, too-large-block, and unsupported-type notices are the points where users decide whether a diagram actually rendered or why it was skipped.
• /pi-mermaid empty-state messages tell users whether there was no assistant message or no Mermaid block.
• I kept this to runtime status/command copy only; no README or generated files.

What changed:

• adds a tiny optional i18n bridge with English fallbacks
• adds es/fr/pt-BR bundles for render status and /pi-mermaid empty states
• includes i18n.ts in the package files list so the runtime import is packaged
• preserves current behavior when no i18n provider is present

Validation:

• npx tsc --noEmit --module ESNext --moduleResolution Bundler --target ES2022 --skipLibCheck --allowImportingTsExtensions index.ts passed
• npm pack --dry-run passed

If useful later, I’m happy to handle broader localization in small follow-up PRs using whatever locale set you prefer.