Design a common skill entry point that routes users to the right step-specific skill

## Problem

The Azure SDK Tools Agent (`azsdk-cli`) ships a number of skills that target specific steps in the SDK lifecycle (TypeSpec authoring, SDK generation, release planning, APIView, etc.), but there's no single entry-point skill that helps the agent quickly figure out *where in the process* a team currently is and route them to the right next skill.

Today the agent has to guess, or the user has to know to ask for a specific skill by name.

## Proposal

Add a top-level "entry point" / "router" skill that:

- Inspects the user's current workspace / repo state
- Asks a short series of triage questions if needed
- Identifies which step of the SDK lifecycle the team is on (spec authoring → spec review → SDK generation → SDK customization → release plan → release)
- Points the user (and the agent) at the right next skill for that step

This makes the agent feel like a single coherent guide instead of a bag of unrelated skills, and reduces "I didn't know that skill existed" misses.

## Notes

- Originally captured as a brain-dump draft during the SDK team → evals team handoff. Promoted to a real issue so it can be tracked alongside other tools-agent work.
- Should be designed to coexist with any existing AGENTS.md-driven entry points in the repos where the agent is installed.

/label "AzSDK Tools Agent"

Start by examining the existing azsdk-cli skills and the AGENTS.md-driven entry points mentioned in the issue. Map the current SDK lifecycle skills from TypeSpec authoring through release, then define the router's triage questions and routing behavior. Done means a top-level skill directs users to the appropriate next step without conflicting with existing repository entry points.

Written by the indexing model from the issue text.