feat: support interactive login to DIAL toolset #191

[ypldan]

Applicable issues

• fixes Support interactive login into DIAL Toolset #191

Description of changes

When a DIAL MCP toolset requires authentication, QuickApp now requests interactive sign-in from the user mid-request instead of failing with an error.

How it works: If an MCP server returns 401 during initialization or tool execution, QuickApp calls DIAL Core's /v1/ops/client-channel/interact endpoint — which notifies the client (via a pre-established SSE channel) to complete login. On success, the failing operation is retried once.

Key design decisions:

• During initialization, all 401 failures are collected and sent as a single batched interact request — so the user sees one prompt even if multiple toolsets need login.
• During tool execution, each tool handles its own 401 independently (DIAL Core deduplicates server-side).
• The SDK's built-in heartbeat_interval keeps the response stream alive during the wait.
• Only DialMCPToolSet participates; plain MCPToolSet and requests without X-DIAL-CLIENT-CHANNEL-ID are unaffected.

Full design: docs/designs/interactive_login.md

Checklist

• Title of the pull request follows Conventional Commits specification
• Design documented is updated/created and approved by the team (if applicable)
• Documentation is updated/created (if applicable)
• Changes are tested on review environment
• Integration tests pass

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