fix(docs): harden GEO discovery endpoints

[zahlekhan]

What

• Upgrades /llms.txt from a generic relative-link list to a structured OpenUI index with project identity, an approved summary, grouped resources, absolute Markdown URLs, and canonical HTML sources.
• Adds canonical source attribution to individual and aggregate LLM-readable documentation.
• Returns explicit UTF-8 content types, an HTTP canonical Link header for Markdown copies, and noindex, follow for the aggregate /llms-full.txt document.
• Adds deterministic GEO-output validation and runs it with docs type checking in CI.

Why

The existing LLM-facing routes were accessible, but they did not provide enough project context or protocol-level canonicalization. That made the output less useful to agents and allowed Markdown copies to look like indexable duplicates of the HTML documentation.

Scope

This PR contains only the documentation GEO fix and its direct test, dependency, lockfile, and CI support. It does not include the autoresearch control plane, DataForSEO, PostHog, Codex adapters, analytics changes, SEO platform work, or unrelated UI changes.

Validation

• pnpm --filter @openuidev/docs test:geo — 6 tests
• pnpm --filter @openuidev/docs types:check
• Targeted ESLint and Prettier checks
• pnpm install --lockfile-only --frozen-lockfile --offline --filter @openuidev/docs
• git diff --check upstream/main...HEAD
• Local route verification:
  • /llms.txt → 200, text/plain; charset=utf-8
  • /docs/openui-lang/quickstart.mdx → 200, text/markdown; charset=utf-8, canonical Link
  • /llms-full.txt → 200, X-Robots-Tag: noindex, follow