Qualify external auth methods and keyless local availability

[piclaw-bot]

External auth-method evidence and keyless local availability

Refs #1458 and #1442; both stay open. This consolidated offline AUTH-06 slice follows merged custom-storage #1477.

• Test public exact-0.99.1 Bedrock/Vertex/Azure auth methods using injected synthetic environment/file contexts: stored/ambient precedence, profile/static-key recognition, ADC/service-account setup and API-key metadata.
• Fix composed keyless Ollama/llama.cpp availability using the upstream dummy-key convention. Only those two IDs get a non-secret configuration marker when no submitted or usable stored key exists; no marker enters credential storage.
• Verify SDK availability, reopen, update and removal for both local IDs, and authenticated-local blank updates retaining real stored keys without a marker.

This does not qualify cloud credential-chain execution, metadata/token exchange, actual local endpoint/header behavior, optional managed-identity bootstrap, legacy-key migration, cross-process config transactions, full CLI/device/Delegate/live accounts. No inference, deployment or restart.

Validation

External methods: 8 pass, 35 assertions. Post-merge method/inventory: 12/114. Combined local/custom/external/handler set: 39/313; five types, strict fixture types, scoped lint and independent rereview pass. Marker allowlist/legacy guard and stored-key preservation covered. The frozen canonical gate passed 5,951 runtime tests, seven existing skips and no failures, plus 25 feature and nine web checks. Pack hygiene passed 24,741 files. Final five types and diff checks passed at baseline c8e349299; unchanged 95-diagnostic compose baseline. Private Bun cache, shared-cache permissions unchanged.