chore(docs): correct generated descriptions, mcp context, and core install

[coryrylan]

Summary

• Preserve explicitly authored page descriptions, and stop the shared metadata generator from adding a period after an arbitrary cutoff.
• Give the Button overview, API, and examples pages distinct descriptions, and publish those strings in the HTML meta description, Open Graph description, and JSON-LD.
• Point llms.txt and llms-full.txt at a generated MCP context page, https://nvidia.github.io/elements/context/mcp.md, while the CLI link stays on /context/cli.md.
• Remove the local .npmrc and npm login steps from the @nvidia-elements/core getting-started flow, and add react, vue, and angular as integration-target keywords.

Verification

• mise exec -- pnpm exec vitest run --config=vitest.config.ts src/_11ty/layouts/metadata.test.ts src/_11ty/plugins/llms-txt.test.ts — 44 passed
• mise exec -- pnpm run build in projects/site
• pnpm pack for @nvidia-elements/core — packaged README has the public install command and no login step; packaged keywords include react, vue, and angular
• Generated homepage description ends with autonomous vehicle UI.
• Generated MCP HTML renders the button validation example and prompt examples

  

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[github-code-quality]

Code Coverage Overview

Languages: TypeScript

TypeScript / code-coverage/vitest

The overall line coverage in commit 43896e5 in the cursor/docs-discover... branch remains at 99%, unchanged from commit 7a82fb5 in the main branch.