Add skills for webpubsub service

[zackliu]

Description

Add the initial azure-webpubsub skill with focused guidance for webpubsub best practice.

Checklist

• [x ] Tests pass locally (cd tests && npm test)
• [x ] If modifying skill descriptions: verified routing correctness with integration tests (npm run test:skills:integration -- <skill>)
• [x ] If modifying skill USE FOR / DO NOT USE FOR / PREFER OVER clauses: confirmed no routing regressions for competing skills
• [x ] Version bumped in skill frontmatter (if skill files changed)

Related Issues

[kvenkatrajan]

Consider consolidating this under azure-messaging with separate reference files for pubsub. Please note if there are troubleshooting workflows consider consolidating those reference files under azure-diagnostics. Here's a reference file - #1986

[zackliu]

@kvenkatrajan Thanks for the suggestion. My concern is that the two skills have very different scopes.

azure-messaging is primarily troubleshooting-oriented today and it's primary for eventhub and servicebus, while the Web PubSub content here is mostly best-practice and design guidance. If we put them into the same skill file, I worry they will interfere with each other during routing and prompt activation, and the mixed intent may reduce answer quality.

I think a cleaner approach is to keep troubleshooting content consolidated where appropriate, but keep Web PubSub best-practice guidance separate.

[jongio]

Issues to address:

• SKILL.md:15-16 - Quick Reference lists 3 MCP tools but the MCP Tools section (line 28-30) only documents one. An agent won't know when to use monitor or resourcehealth for Web PubSub.
• triggers.test.ts, unit.test.ts - missing trailing newline

Merge conflict in skills.json needs a rebase (main now includes entra-agent-id).

[jongio]

Addresses my previous feedback. Merge conflict resolved, MCP tools table is now consistent, Entra ID roles documented per @JialinXin's suggestion. Looks good.

cc @kvenkatrajan for approval

[zackliu]

@jongio Please help to merge.