Fxa 12118

[vbudhram]

Because

• Users refreshing the confirmation code page during Firefox Sync OAuth flow saw "Bad Request" error
• In-memory OAuth keys (keyFetchToken, unwrapBKey) are lost on page refresh with no recovery path

This pull request

• Adds useOAuthFlowRecovery hook to recover from interrupted OAuth Native flows via Firefox webchannel
• Adds fxaOAuthFlowBegin and fxaOAuthFlowIsActive commands to firefox.ts
• Updates SigninTokenCode and ConfirmSignupCode to attempt recovery when state is missing
• Redirects to /signin with fresh OAuth params on successful recovery

Issue

Closes: https://mozilla-hub.atlassian.net/browse/FXA-12118

Checklist

• My commit is GPG signed
• Tests pass locally (if applicable)
• Documentation updated (if applicable)
• RTL rendering verified (if UI changed)

Other Information

How to test:

1. Open Firefox → Settings → Sync → Sign in
2. Enter credentials, reach confirmation code page
3. Refresh the page (F5)
4. Should redirect to /signin instead of "Bad Request" error

Note: Requires Firefox with fxaccounts:oauth_flow_begin webchannel support

YOu can download it here: https://drive.google.com/file/d/1oKZHHJXqJ5C0LniU-iJwxnLoCQE1FvWt/view?usp=drive_link