docs: add Spanish translation for README quickstart

[OMEE-Y]

Summary

Adds a Spanish translation of the repository's Quickstart guide by creating a dedicated README.es.md file at the root level. This helps accessibility for Spanish-speaking marketing engineers looking to implement Dualmark infrastructure.

Changes

• Added README.es.md in the root directory containing the fully translated Quickstart documentation for Astro, Next.js, and Cloudflare Workers adapters.
• Maintained exact framework configuration parameters, code blocks, terminal commands, and structural markdown anchors from the primary documentation to ensure code parity.

Type

• Bug fix (non-breaking)
• New feature (non-breaking)
• Breaking change
• Spec change (requires bump in AEO_SPEC_VERSION)
• Docs / examples / tooling only

Verification

• bun run build passes
• bun run test passes
• bun run typecheck passes
• If touching examples: ran dualmark verify against the example end-to-end
• If touching /spec/: ran bun run --filter dualmark-docs sync-spec and committed the mirror

Changeset

• Added a changeset (bun run changeset) for any package with a user-visible change

[vercel]

@OMEE-Y is attempting to deploy a commit to the Dodo Payments Team on Vercel.

A member of the Team first needs to authorize it.

[OMEE-Y]

Closes #22