docs(intro): state the $DIG North Star ethos in the introduction

[MichaelTaylor3d]

Summary

• Adds a callout to the top-level introduction stating DIG Network's ethos: $DIG is the engine and economy of the network — every value exchange (publishing a capsule, owning a store, tipping a creator) flows through $DIG, while consuming content stays effortless and free (no charge to read; payments are for publishing and ownership).
• Applied to the English docs/intro.md and all 13 translated locale copies (i18n/{de,es,fr,hi,id,ja,ko,pt-BR,ru,tr,vi,zh-CN,zh-TW}/docusaurus-plugin-content-docs/current/intro.md) — every one of the 14 shipped locales carries the statement, translated to match each file's existing tone/terminology while preserving $DIG/capsule/store/DIG Network verbatim.
• Copy is positive-voice, self-contained, and does not reference any internal project file or task number.
• Version bump: package.json 0.3.21 → 0.3.22 (patch — docs content only, no public-API/behavior change), which also propagates into the generated static/openrpc.json / static/openrpc-node.json version fields via the repo's gen script.

Test plan

• npm run build — builds clean across all 14 locales (onBrokenLinks/onBrokenAnchors: "throw" did not fire); llms.txt/sitemap.xml/robots.txt all present + non-empty in dist/
• npm run typecheck — clean
• npm run test:unit — 1/1 passing
• npm run test:a11y — 22/22 passing (axe WCAG 2.2 AA, ARIA snapshots, keyboard nav, mobile nav)
• npm run test:e2e — 28/28 passing (adds SEO/hreflang/llms.txt checks on top of the a11y set)
• Verified the callout renders identically (same :::info admonition shape) in the English page and all 13 locale copies

Closes #391 (DIG-Network/dig_ecosystem)

Co-Authored-By: Claude noreply@anthropic.com