fix(docs): correct Vue, rrweb, and SPA guides

[cursor]

Findings

Broken

• None. The production build and all link, structure, callout, unsafe-HTML, and reference-link validators pass.

Wrong

• Restore runnable, public-facing React SPA setup guides after internal agent instructions replaced them and dropped the Vite application import.
• Document the published createGT() customMapping option and its exact Vue runtime behavior.
• Correct rrweb locale-cookie fallback, replayer recreation, recorder mounting, and exported type contracts.
• Preserve multi-entry webpack configuration while changing the browser entry.

Polish

• Restore guide frontmatter, numbered steps, stable heading anchors, related-link metadata, and generated related-page handling.
• Add Vue to the drop-in coding-agent guide and document the React SPA source-glob defaults in the canonical Quickstart.

Verification

• Installed and probed gt-vue@0.1.1, gt-rrweb@0.2.0, gt-react@11.1.15, and gt@2.17.0 in fresh projects.
• Built fresh Vue 3.5/Vite 8 and React 19/Vite 8 projects from the documented setup.
• Type-checked the documented rrweb recorder/replayer examples and public type exports.
• Ran the complete content validator suite and pnpm build:content.

Merge

Please squash-merge and enable auto-merge once checks pass.