Probe Bedrock and Vertex provider keys (ADR-0003 follow-up) #15

Why

The current probe layer (src/main/probes/) only knows Anthropic. The catalog has 18 entries but probeProvider() returns error: No probe implemented for "<id>" for any provider whose probeKind is aws, gcp, or azure.

Bedrock and Vertex don't expose a cheap "validate this credential" HTTP endpoint the way OpenAI/Anthropic do — there's no /v1/models you can hit. The standard check is to call a tiny STS-shaped API and parse the response. Three axes:

1. Bedrock — call bedrock:ListFoundationModels (or bedrock:ListCustomModels) with the user's AWS credentials (default chain). 403/expired token ≠ working.
2. Vertex — call aiplatform.googleapis.com/v1/projects/<project>/locations/global/publishers/google/models with the configured ADC + project + region. The envKeys[] for Vertex is empty today so we need to surface a "Project + Region required" step in the wizard before this can be wired.
3. Azure — GET <endpoint>/openai/deployments?api-version=2024-02-01 with the user's AZURE_OPENAI_API_KEY. Or just probe the deployment the user names.

Scope

• Wire aws probe kind: uses SDK's default credential provider chain; minimal IAM sigv4 against bedrock-runtime or bedrock control plane; returns valid | error with the AWS error code surfaced in detail.
• Wire gcp probe kind: takes a project and region from wizard config; uses @google-cloud/aiplatform or just an authenticated REST GET; requires gcloud auth application-default login upstream.
• Wire azure probe kind (and azure-openai): simple GET against the deployment list with the configured key.
• Vault entry for Vertex needs to carry {project, region} alongside the credential. Either widen SecretWriteOptions or surface project/region as separate UI fields in the Keys step.
• Update PROVIDER_CATALOG notes for cloud_creds rows to indicate "wizard will ask for project/region first".
• Renderer Keys step: when user picks Vertex, ask for project id + region before "Save"; persist into vault alongside the credential (or as a sibling secret).
• App + CLI both pick up the same probes via the shared runProbe() dispatcher.

Acceptance criteria

• runProbe({ providerId: 'bedrock' }) returns { valid: true, status: 'ok' } against a working AWS account with Bedrock access.
• Same returns { valid: false, status: 'invalid', detail: 'AWS error: ...' } for an unconfigured credential chain.
• Vertex probe requires a saved project + region; errors sensibly without one.
• Azure probe works against an actual deployment.
• All three appear in the Validate button in the renderer without code changes beyond the probe files.
• Tests (or fixture-mocked HTTP) for at least the error paths.
• npm run typecheck && npm run lint && npm run build clean.

References

• ADR-0003 (docs/adr/0003-key-validity-and-expiry-probing.md)
• AWS SigV4 reference: https://docs.aws.amazon.com/AmazonS3/latest/API/sig-v4-header-based-auth.html
• Vertex aiplatform.googleapis.com: https://cloud.google.com/vertex-ai/generative-ai/docs/learn/rest
• Azure OpenAI REST: https://learn.microsoft.com/en-us/azure/ai-services/openai/reference