fix(skill-creator): trim overlong description and remove hardcoded download path

[krishyaid-coder]

This PR resolves two quality issues in skills/skill-creator/SKILL.md:

1. Description length. The description field was 319 characters, exceeding the ~250-character guideline in the best-practices doc. Trimmed to 187 characters while preserving the three core use-cases (create, modify, evaluate). The explicit trigger phrase remains.

2. Hardcoded user path. Line 371 referenced ~/Downloads/eval_set.json, which assumes macOS conventions and that the browser writes to the user's Downloads folder. On Windows and Linux browsers default elsewhere; the exact path also varies per browser and configuration. Reworded to describe the intent without assuming a location, so the guidance stays portable.

How I found these

Static analysis with doodle, a small MIT-licensed linter for SKILL.md files grounded in the failure modes discussed in #267. Findings correspond to the desc/too-long and body/absolute-user-path rules.

For context, I ran the same tool across 62 published skills as a validation exercise, and the patterns are common enough that it seemed worth surfacing directly against the reference skill authors will most often study when writing their own. Full report: https://github.com/krishyaid-coder/doodle/blob/main/docs/QUALITY_REPORT.md

Happy to close if the direction isn't wanted, or to split into two commits if a smaller-per-commit unit reviews better. Not attached to the specific wording of either replacement but the goal is just alignment with the documented guidelines.