docs: fix 6 documentation issues (#303, #245, #186, #134, #61, #73) (#486)

* docs: fix 6 documentation issues (#303, #245, #186, #134, #61, #73)

Addresses six open documentation issues in a single pass:

- **#303** -- Add `npx agent-browser` usage across README, SKILL.md, docs site, and `--help` output for zero-install experience. Global install is recommended as the fastest path (native Rust CLI vs Node.js indirection with npx).
- **#245** -- Document Claude Code skill installation with `npx skills add vercel-labs/agent-browser`
- **#186** -- Split installation instructions into Global (recommended), Quick Start (npx), and Project (local dependency) sections with clear guidance on when to use each
- **#134** -- Add "Why agent-browser over playwright-mcp?" comparison table to README covering output format, element selection, protocol, sessions, performance, mobile, cloud, and streaming
- **#61** -- Add "Timeouts and Slow Pages" section to SKILL.md documenting the 60s default timeout, all `wait` variants, and guidance for slow websites
- **#73** -- Replace stale `cp node_modules/...` advice with `npx skills add`, add warning against copying SKILL.md manually, add "Session Management and Cleanup" section to SKILL.md

* remove section

* fix doc

docs/src/app/page.mdx

@@ -5,8 +5,11 @@ export const metadata = { title: "agent-browser" }
 Browser automation CLI designed for AI agents. Compact text output minimizes context usage. Fast Rust CLI with Node.js fallback.
 
 ```bash
-npm install -g agent-browser      # all platforms
+npm install -g agent-browser      # all platforms (fastest, native Rust CLI)
 brew install agent-browser        # macOS
+
+# or try without installing
+npx agent-browser open example.com
 ```
 
 ## Features