docs(oauth): point OAuth client OTP to sidebar OAuth setup entry from #2178

[r266-tech]

Summary

Docs catch of #2178 (feat(web-studio): PWA, mobile UI polish, OAuth-setup
tab, request-logs touch-ups; @ZaynJarvis author / @t0saki merger, merged
~13h ago). #2178 extracted the OAuth client OTP form out of the
Studio "Connection & Identity" dialog (connection-dialog.tsx shrinks by
~200 lines) into a new OAuthSetupDialog reached from a dedicated
OAuth setup entry in the sidebar footer (opens dialog on >=md,
routes to /studio/oauth/setup on phone).

docs/{en,zh}/guides/11-oauth.md still tells users to "use the OAuth
client OTP block at the bottom of the Connection & Identity dialog" /
"在 Studio 的『连接与身份』对话框底部就有 OAuth client OTP 区块". After
#2178 that block lives in the new OAuth setup entry instead — the
connection dialog now only handles API-key / identity input (the file
contains zero OTP mentions post-#2178).

This PR retargets the two stale callouts (one in How it works push-OTP
paragraph, one in Quick start (HTTP, local only) step 4) in both EN
and ZH guides to point users at the new sidebar footer OAuth setup
entry / /studio/oauth/setup route.

Test plan

• Ran the existing dual-doc EN/ZH mirroring convention check (both
  guides updated symmetrically at matching positions).
• Verified i18n label match: navigation.oauthSetup.title = 'OAuth setup' (en) / 'OAuth 设置' (zh-CN), matching the wording used in
  the docs.
• Verified app-shell.tsx sidebar footer has the new
  openOAuthSetup menu item (with KeyRoundIcon) wired to either
  OAuthSetupDialog (>=768px) or navigate({ to: '/oauth/setup' })
  fallback.
• Verified connection-dialog.tsx no longer contains any OTP
  references after feat(web-studio): PWA, mobile UI polish, OAuth-setup tab, request-logs touch-ups #2178.

Pure docs change, no behavioral impact.

[github-actions]

PR Reviewer Guide 🔍

Here are some key observations to aid the review process:

🎫 Ticket compliance analysis ✅ 2178 - Fully compliant Compliant requirements: Updated OAuth docs to reflect new OAuth setup entry in sidebar footer Retargeted stale callouts from Connection & Identity dialog to new OAuth setup entry Updated both English and Chinese guides symmetrically

⏱️ Estimated effort to review: 1 🔵⚪⚪⚪⚪

🏅 Score: 100

🧪 No relevant tests

🔒 No security concerns identified

✅ No TODO sections

🔀 No multiple PR themes

⚡ No major issues detected

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