docs: realign drifted sequence diagrams with current SDK behavior

[Copilot]

The weekly sequence-diagram audit flagged multiple Mermaid docs under docs/ that no longer matched implementation behavior. This PR updates those diagrams to reflect current runtime flows and component boundaries, without changing product code.

• CloudAdapter pipeline diagrams

  • Narrowed blocking-path condition to DeliveryMode == Stream (removed ExpectReplies/Invoke from SSE path).
  • Updated call-chain depiction to RunPipelineAsync -> ReceiveActivityWithStatusAsync.
  • Added IActivityTaskQueue to the normal-path view and corrected completion ownership to CloudAdapter.

• OAuth / Teams SSO flow diagrams

  • Removed short-circuited IsValidActivity() steps for forceSignIn=true paths.
  • Corrected invoke error branch (ResetStateAsync, no _userSignInFailureHandler on invoke turn).
  • Updated token-cache decision conditions (agentic-request path included).
  • Corrected SignInState storage key and timeout invoke behavior notes.
  • Updated consent-required Teams SSO continuation to a second signin/tokenExchange + ExchangeToken() flow; fixed UserAuthorization source path.

• Proactive messaging diagram

  • Clarified that the full-turn behavior comes from Proactive.ContinueConversationAsync using ProcessProactiveAsync plus OnTurnAsync, not adapter ContinueConversationAsync alone.

• Serialization extension diagram

  • Replaced non-existent Teams converter example with actual SharePoint converters (AceDataConverter, AceRequestConverter).

• StreamingResponse diagram terminology

  • Replaced A2A/Agent-to-Agent labels with canonical DeliveryModes.Stream SSE wording in channel and StreamId descriptions.

Example of the core drift correction pattern:

sequenceDiagram
    Client->>CloudAdapter: POST /api/messages
    alt DeliveryMode == Stream
        CloudAdapter->>HttpResponse: ResponseBegin(text/event-stream)
    else DeliveryMode == Normal
        CloudAdapter->>IActivityTaskQueue: QueueBackgroundActivity(activity)
    end

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[MattB-msft]

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