docs: search keywords so pricing and npx skills searches find their answers (#6472)

Mintlify search keywords on the FAQ (pricing, price, cost, free...) and
the skills guide (npx skills, skills add...). Last week pricing searches
found a clicked result 8% of the time and npx skills 0%.

docs/faq.mdx

@@ -2,6 +2,7 @@
 title: "HyperFrames FAQ"
 sidebarTitle: "FAQ"
 description: "Short answers to the questions people ask most about HyperFrames: cost, which agent to use, Windows, Studio, Remotion, rendering, audio, and fonts."
+keywords: ['pricing', 'price', 'cost', 'free', 'paid', 'subscription', 'plan', 'how much']
 ---
 
 Short answers to the questions people ask the docs assistant most often. Each

docs/guides/skills.mdx

@@ -2,6 +2,7 @@
 title: "Install and update agent skills"
 sidebarTitle: "Agent skills"
 description: "Teach a coding agent how to create valid HyperFrames projects."
+keywords: ['npx skills', 'npx skills add', 'skills add', 'install skills', 'update skills']
 ---
 
 import { DocsVideo } from "/snippets/docs-video.jsx";