Simplify auth login help text, document query parameter support

[simonfaltum]

Why

The auth login help text was verbose and redundant. Four numbered scenarios all described the same core behavior (profile is created or updated) with minor variations, and each repeated the "databricks-cli" auth type implementation detail. The help text also didn't mention URL query parameter support (?o=, ?account_id=).

Changes

Before: ~40 lines of help text with four near-identical scenarios explaining profile update behavior, specific SDK names that will go stale, and no mention of query parameter support.

Now: ~20 lines. Drops the redundant scenarios in favor of one sentence ("If a profile with the given name already exists, it is updated. Otherwise a new profile is created."). Adds documentation for URL query parameters (?o=<workspace_id>&account_id=<id>) with a shell quoting note. Replaces specific SDK list with generic "SDKs".

Test plan

• make checks passes
• databricks auth login --help shows updated text
• No functional changes, help text only

[github-actions]

Suggested reviewers

Based on git history of the changed files, these people are best suited to review:

• @pietern -- recent work in cmd/auth/
• @tanmay-db -- recent work in cmd/auth/

Confidence: low

Eligible reviewers

Based on CODEOWNERS, these people or teams could also review:

@andrewnester, @anton-107, @denik, @shreyas-goenka

_{Suggestions based on git history of 1 changed files (1 scored). See CODEOWNERS for path-specific ownership rules.}