feat(grok): add opt-in --web flow for grok ask

[KasumiChen]

Summary

• preserve the existing default opencli grok ask behavior
• add an explicit --web flag for the hardened browser-backed consumer web flow
• update Grok docs/examples to make the default vs opt-in web path clear

Compatibility

• default opencli grok ask --prompt ... remains the existing/default implementation
• only opencli grok ask --prompt ... --web activates the newer grok.com consumer web path
• existing main args and default response shape stay intact by default

Notes

• the --web flow requires an already-authenticated grok.com browser session
• this is still consumer-web automation and may be brittle around auth/session/challenge or DOM changes

Validation

• npx tsc --noEmit
• npx vitest run src/clis/grok/ask.test.ts
• npm run build
• npx tsx src/main.ts grok ask --prompt "Reply with exactly OK and nothing else." --web -f json