feat(auth): enable OS port selection for OAuth server Use port 0 to …

[harsha08-2k6]

…allow OS to automatically assign available port, removing hardcoded port range (8000-8010) from _prepare_server method. This resolves port conflict issues when the OAuth server fails to bind to predefined ports. Fixes #913

Refactor server preparation to use a dynamic port.

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PR check list

• [ ] As much as possible, the changes include tests (unit and/or functional)
• [ ] If the changes affect the end user (new feature, behavior change, bug fix) then the PR has a changelog entry (see doc/dev/getting-started.md). If the changes do not affect the end user, then the skip-changelog label has been added to the PR.

[sevbch]

Also, please make sure to add a test for the feature you're adding. I'll let you ask for reviews when all of this is done.