docs: drop the WEBUI_URL step from the browser search tutorial and correct the sidebar, API key and IPEX pages

[silentoplayz]

Summary

I compared the browser search engine, Firefox sidebar, iTerm2, Continue and IPEX-LLM pages with the frontend and the config defaults.

• Browser search engine: the integration is browser-side. The page URL's q parameter is what Open WebUI reads, and WEBUI_URL plays no part, so the WEBUI_URL step and the two related bullets are replaced.
• Firefox sidebar: the URL parameter list gains submit=false, load-url, image-generation and code-interpreter.
• iTerm2 and Continue: API keys are off by default and may be limited by endpoint restrictions.
• IPEX-LLM: the toast strings are current ("Server connection verified"), and the Docker default Ollama URL is noted.

Related issue or discussion

None.

Checklist

• I have reviewed the relevant documentation and matched the existing style.
• This PR meets Open WebUI's contribution standards: it is accurate, relevant to users, narrowly scoped, maintainable, and not promotional content, advertising, lead generation, SEO placement, or a request to list a product, service, provider, integration, gateway, tool, or company primarily for visibility.
• I understand that PRs that do not meet these standards may be closed without review and will not be merged. Repeated, low-quality, off-topic, promotional, or intentionally misleading submissions may result in the contributor being blocked from future participation in Open WebUI repositories.

Notes for reviewers

Sources on dev: src/lib/components/chat/Chat.svelte (searchParams handling), config.py (ENABLE_API_KEYS, endpoint restrictions, OLLAMA_BASE_URL), src/lib/i18n/locales/en-US/translation.json, and AddConnectionModal.svelte.