fix(auth): trim OAuth credentials during setup

[y4ho0]

Description

Closes #882.

Interactive OAuth setup now trims leading and trailing whitespace from pasted Client IDs and client secrets before validation and persistence. Whitespace-only values are rejected as empty, while characters inside a credential are preserved.

This prevents invisible spaces or newlines copied from Google Cloud Console from producing an invalid_client response during login.

Dry Run Output: Not applicable; this changes interactive credential input and does not create a Discovery API request.

Validation

• cargo fmt --all -- --check
• cargo test --workspace -- --test-threads=1 (785 tests passed)
• cargo clippy -- -D warnings -A clippy::collapsible_match
• cargo clippy -- -D warnings is currently blocked on unchanged main-branch code at helpers/script.rs:173 by the Rust 1.97 collapsible_match lint

Checklist:

• My code follows the AGENTS.md guidelines (no generated google-* crates).
• I have run cargo fmt --all to format the code perfectly.
• I have run cargo clippy -- -D warnings and resolved all warnings. See the documented pre-existing main-branch warning above; the changed code is clean.
• I have added tests that prove my fix is effective or that my feature works.
• I have provided a Changeset file to document my changes.

[changeset-bot]

🦋 Changeset detected

Latest commit: cb7c6a9

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@googleworkspace/cli	Patch

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[google-cla]

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[y4ho0]

The individual CLA check now passes, and the branch remains mergeable. CI, Coverage, Policy, Release, and the Actions security scan are still in action_required, pending maintainer approval for this first-time fork contribution. Could a maintainer approve those runs when convenient? I’m ready to address any CI or review feedback.