[oauth] add sso->oauth fall back in channels and attribute sign in failure invokes to sso in multi connection

[MehakBindra]

Code improvements and refactoring:

• Improved multi-connection SSO failure handling: signin/failure is now attributed to the connection with a pending SSO sign-in, so the failure callback no longer fires on non-SSO connections.
• Restricted silent SSO to conversations where it can succeed (skipped in channels), falling back to the interactive sign-in button elsewhere.
• Kept OAuth-specific attribution logic out of the general Context type, while keeping the connection-agnostic GetConnectionStatusAsync available (non-obsolete) on it.
• Rewrote the OAuth/SSO design docs for readability and removed the obsolete SsoBot sample.

[azure-pipelines]

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[Copilot]

Pull request overview

This PR removes the SsoBot sample and associated SSO/OAuth documentation artifacts, while refining the OAuthFlow / Context OAuth APIs and the signin/failure routing logic to better attribute silent-SSO failures to the correct connection.

Changes:

• Remove the SsoBot sample (project + sources + settings) and drop it from core.slnx.
• Improve OAuth flow behavior and routing: omit token-exchange data in certain conversation contexts, and route signin/failure via a “pending SSO sign-in” resolver instead of “most recent sign-in”.
• Update docs and samples to reflect the new/cleaned API surface; add unit tests for the updated sign-in card behavior.

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
core/test/Microsoft.Teams.Apps.UnitTests/OAuthFlowTests.cs	Adds tests validating whether OAuth cards include/omit tokenExchangeResource based on conversation type.
core/src/Microsoft.Teams.Apps/OAuth/OAuthFlowExtensions.cs	Changes signin/failure dispatch to resolve the flow with a pending SSO sign-in instead of “most recent sign-in”.
core/src/Microsoft.Teams.Apps/OAuth/OAuthFlow.cs	Adds pending-SSO tracking and adjusts OAuth card construction (conversation-type-based behavior).
core/src/Microsoft.Teams.Apps/Context.cs	Promotes GetConnectionStatusAsync as the generic status API (removes obsolete marker and simplifies flow selection).
core/samples/OAuthFlowBot/Program.cs	Updates the status command to use context.GetConnectionStatusAsync() instead of flow-specific status.
core/docs/sso/security-audit-oauthflow-2026-04-22.md	Removes the OAuthFlow-specific security audit document.
core/docs/sso/oauthflowbot-trace-2026-04-22-summary.md	Streamlines the trace summary by removing SsoBot comparison/bug-fix notes.
core/docs/sso/OAuthFlow-Design.md	Condenses and refreshes the OAuthFlow design documentation (including multi-connection routing notes).
core/core.slnx	Removes the SsoBot project from the solution.
core/samples/SsoBot/SsoBot.csproj	Deletes the SsoBot sample project.
core/samples/SsoBot/Program.cs	Deletes the SsoBot sample implementation.
core/samples/SsoBot/appsettings.json	Deletes the SsoBot sample configuration.

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[corinagum]

Approved pending links fix

[singhk97]

lgtm