chore(cli): delete dead shared/auth layer and inline single-caller pass-throughs

[kanadgupta]

Summary

A shallow-module audit of apps/cli found two kinds of cleanup. Each candidate was checked with the deletion test: remove the module and paste its body into every caller. If the callers end up no longer, the module was only passing work through.

Dead code. Knip did not flag these because each file's only importer was its own colocated unit test.

• The superseded auth layer under apps/cli/src/shared/auth/ (api, crypto, credentials, platform-api, token, errors). Live replacements are src/auth/command-*.ts and src/command-internal/login-*.layer.ts.
• shared/config/cli-project-local-service-versions.{service,layer}.ts, plus the two matching die-placeholders in run.ts and the mock in tests/helpers/mocks.ts.
• shared/output/table.ts and shared/output/time.ts.

Pass-throughs inlined or merged.

• db-connection.layer.ts was a two-line alias; the sql-pg layer now exports dbConnectionLayer directly.
• OutputFormatFlag moves into command-internal/global-flags.ts with the other globals.
• The region display table is hoisted once to command-internal/region.format.ts and shared by backups and projects.
• changedLinkedLocalFlags is called directly by seed and storage instead of through per-command aliases; its coverage moves to the db-target-flags unit test.
• tracing.service.ts, db-bootstrap/messages.ts, standalone-analytics-config.layer.ts, supabaseHome(), output/bold.ts, go-string.ts, report.layers.ts, and prepare.options.ts are inlined at their single caller.
• packages/cli-test-helpers exports harness.ts directly instead of through a barrel.

Follow-up cleanups in later commits.

• The error-tag stability snapshot (src/shared/telemetry/__fixtures__/error-tags.txt) drops the four tags that belonged to the deleted modules: ApiError, InvalidLocalServiceVersionsStateError, InvalidTokenError, and PlatformAuthRequiredError. None of them reached production telemetry.
• Docs that referenced the removed code are updated: the apps/cli/README.md architecture list now points at src/auth/ and describes what remains in src/shared/auth/; apps/cli/docs/tracing-monitoring.md no longer names a Tracing service; apps/cli/docs/code-structure.md uses live symbols in its naming examples; and the db start side-effects note points at start-database.ts for the startup messages.
• docs/self-documenting-cli.md was an orphaned copy still describing the long-removed --usage and --skill flags and guide templates. It now covers only the generate-docs.ts script and the Fumadocs site that exist today.

No behaviour change. Span names and telemetry command paths are unchanged.

Linear: CLI-2606

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