Add ASP.NET Core PR attention canvas

[PureWeen]

Summary

• adds the project-scoped ASP.NET Core Team App canvas backed by the deterministic PR Attention skill
• presents separate Review now and Needs rescue lanes, a compact Ready to merge strip, and expandable secondary classifications
• adds read-only Open PR, Review, and Investigate rescue actions with opaque server-owned item IDs, stale-safe snapshots, and same-origin loopback protection

Validation

• node --test .github/extensions/aspnetcore-team-app/*.test.mjs (18 tests)
• extension reload and inspection succeeded with no provider errors
• live Blazor snapshot completed with query.complete: true across 339 open pull requests

Stack

This PR is stacked on pureween-pr-attention-queue-skill, the branch for dotnet#69040. Review this after the skill PR; retarget it to main after the base lands.

[PureWeen]

Superseded by dotnet#69063.