Deprecate auth env + ensure the cmd uses resolved auth context

[simonfaltum]

Why

auth env had its own custom auth resolution logic (local --host/--profile flags, manual profile-to-host matching via ini file scanning). It didn't go through the standard CLI auth chain, so it couldn't resolve auth from bundle context, default profiles, or environment variables. It was effectively a standalone tool that only worked with explicit profile or host arguments.

The command should return the environment variables needed to authenticate as the exact same identity the CLI is currently authenticated as.

Changes

Refactored to use the CLI's standard auth resolution (root.MustAnyClient + cmdctx.ConfigUsed), same pattern as auth describe. Uses auth.Env(cfg) from libs/auth/env.go to generate env vars. This means it now works with bundle context, env var auth, default profiles, and all other standard auth paths.

Before: databricks auth env --host https://my-workspace.cloud.databricks.com with custom profile matching.
Now: databricks auth env returns the env vars for whatever identity the CLI resolved through its normal auth chain.

Also adds --output text support for KEY=VALUE lines with proper shell quoting, and hides the command from databricks auth --help listings (still invokable, --help still works).

JSON shape is preserved ({"env": {...}}) to avoid breaking downstream scripts.

Breaking changes:

• Removed command-specific --host and --profile flags (the inherited flags from the parent auth and root commands cover this)
• Only the primary env var per attribute is emitted (via auth.Env, consistent with bundle run)

Structure:

• Formatting extracted into a pure writeEnvOutput(w, envVars, textMode) function; the Cobra RunE is a thin adapter. Follows the decoupling patterns from go-code-structure.md (principles 1 and 5).

Removed ~120 lines of dead code: canonicalHost, resolveSection, loadFromDatabricksCfg, collectEnvVars, ErrNoMatchingProfiles.

Test plan

• Unit tests for text and JSON output modes (via writeEnvOutput directly, no Cobra setup required)
• Unit tests for shell quoting: spaces, special chars, single quotes, newlines
• NEXT_CHANGELOG.md entry added
• Existing cmd/auth tests pass; make checks and full golangci-lint clean
• Manually verified against --profile e2-dogfood: JSON shape matches prior v0.296.0 behavior, all expected env vars present (DATABRICKS_HOST, DATABRICKS_ACCOUNT_ID, DATABRICKS_CONFIG_PROFILE, DATABRICKS_WORKSPACE_ID, etc.), text mode emits sorted shell-quoted KEY=VALUE lines
• Verified env no longer appears under databricks auth --help, but databricks auth env --help still works

[github-actions]

Approval status: pending

/cmd/auth/ - needs approval

Files: cmd/auth/env.go, cmd/auth/env_test.go
Suggested: @mihaimitrea-db
Also eligible: @tanmay-db, @tejaskochar-db, @hectorcast-db, @renaudhartert-db, @parthban-db, @Divyansh-db, @chrisst, @rauchy

General files (require maintainer)

Files: NEXT_CHANGELOG.md
Based on git history:

• @denik -- recent work in ./, cmd/auth/

_{Any maintainer (@andrewnester, @anton-107, @denik, @pietern, @shreyas-goenka, @renaudhartert-db) can approve all areas.
See OWNERS for ownership rules.}

[simonfaltum]

Closing in favor of #5049, which is a much smaller, deprecation-only change (9 lines added across 2 files) without the refactor and new output modes that muddied this PR.