docs: add product usage and operations guides

docs/.gitignore

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+
+node_modules/
+dist/
+
+.vite/
+coverage/
+*.tsbuildinfo
+
+*.log
+npm-debug.log*
+pnpm-debug.log*
+yarn-debug.log*
+yarn-error.log*
+
+.DS_Store
+Thumbs.db
+
+.env
+.env.local
+.env.*.local
+
+src/generated/
+
+# Generated runtime artifacts
+public/search-index-*.json
+public/changelog-index-*.json
+public/doc-git-meta.json
+public/llms.txt
+public/llms-full.txt
+public/feed.xml
+public/sitemap.xml
+public/access/