Add assistant provider selection and explicit sign-in

[niksacdev]

Summary

Assistant setup previously required an existing copilot_agent endpoint. Settings and CLI now support a dedicated GitHub Copilot device sign-in, explicit model discovery, an existing endpoint, or a Foundry model deployment using Azure CLI authentication.

Existing endpoint selections and explicit disablement survive migration. New setups default to Copilot; saved settings contain provider choices rather than credentials. Connection tests are tied to the selected configuration, and assistant-proposed mutations still require exact host confirmation.

Updates the product and architecture documentation to describe the current trial/campaign workflows and distinguish local VLA action inference from the separate ABC simulator episode integration.

Validation

• Installed pre-commit hooks, including the complete Python regression suite.
• 234 UI behavior tests; JavaScript syntax, Ruff, Bandit, and Python compilation.
• Controlled pinned Copilot SDK/CLI tests, including telemetry and process cleanup.
• Mock evidence demo and both CI campaign examples.
• Python and npm dependency audits; secret scanning; 461 relative documentation links.

Authenticated GitHub/Azure inference and model quality remain unverified; authentication/provider behavior has controlled regression coverage.