Skill descriptions exceed agent tool character budget

Agent tools have a hard char count budget for how many skills it can put in its context. For example, Copilot CLI has a pre-defined 15000 char count budget. If the aggregated char count of all skills exceed this budget, Copilot CLI may truncate any skill at runtime, causing inconsistent behavior.

A PR check is added to count the aggregated char count of all skills in this repo and compares it against Copilot CLI's default budget.

If you are adding a new skill, consider the following:
- Can the content be added as a reference to an existing skill?
- Can an existing skill be rebranded (e.g. change skill name and description) and cover the new content?
- Can the description of the new skill made more concise?

No files or tests are named. Start by locating the PR check and the repository's skill files, then determine how their aggregate character count is calculated and compared with Copilot CLI's 15,000-character budget. Done means the check reliably flags an over-budget aggregate and permits content within the limit.

Written by the indexing model from the issue text.