[TypeSpec Authoring] Assess assessment skill agent friendliness

## Parent issue

Part of #14529.

## Goal

Assess and improve the TypeSpec assessment skill's agent friendliness so agents can discover, invoke, interpret, and act on it reliably.

## Scope

- Define agent-friendliness criteria for skill routing, instructions, tool usage, outputs, errors, and mitigation handoffs.
- Evaluate whether an agent can select the correct assessment mode and supply required inputs without undocumented assumptions.
- Identify ambiguous, duplicated, or overly long instructions that cause inconsistent agent behavior.
- Assess whether reports and structured outputs make findings, evidence, incomplete analysis, and next actions unambiguous to an agent.
- Create prioritized improvements and regression cases for identified gaps.

## Acceptance criteria

- Agent-friendliness criteria and representative scenarios are documented.
- The initial skill is assessed against each criterion with evidence.
- Findings distinguish routing, instruction, execution, output-contract, and recovery issues.
- Each confirmed gap has a linked improvement or benchmark task.

No files or tests are named in the issue. Start with the TypeSpec assessment skill and parent issue #14529, then define assessment criteria and representative scenarios before evaluating routing, instructions, execution, outputs, and recovery. Done means documented evidence, prioritized improvements or benchmark tasks, and a linked improvement for every confirmed gap.

Written by the indexing model from the issue text.