Plugin skill name validation rejects skills with qualified name > 64 chars

Description

The build-web-data-visualization curated plugin has 8 skills that are silently skipped during loading because their qualified names (plugin_name:skill_name) exceed the 64-character maximum.

Repro

On a system with the build-web-data-visualization plugin installed (version 94a36683), Codex emits:

⚠ /Users/.../skills/accessibility-and-inclusive-visualization/SKILL.md: invalid name: exceeds maximum length of 64 characters
⚠ /Users/.../skills/dashboards-and-real-time-visualization/SKILL.md: invalid name: exceeds maximum length of 64 characters
⚠ /Users/.../skills/geospatial-and-cartographic-visualization/SKILL.md: invalid name: exceeds maximum length of 64 characters
⚠ /Users/.../skills/grammar-of-graphics-and-declarative-visualization/SKILL.md: invalid name: exceeds maximum length of 64 characters
⚠ /Users/.../skills/scrollytelling-and-parallax-data-visualization/SKILL.md: invalid name: exceeds maximum length of 64 characters
⚠ /Users/.../skills/statistical-and-uncertainty-visualization/SKILL.md: invalid name: exceeds maximum length of 64 characters
⚠ /Users/.../skills/typescript-data-visualization-engineering/SKILL.md: invalid name: exceeds maximum length of 64 characters
⚠ /Users/.../skills/uml-and-software-architecture-visualization/SKILL.md: invalid name: exceeds maximum length of 64 characters
⚠ Skipped loading 8 skill(s) due to invalid SKILL.md files.

Root cause

The plugin name build-web-data-visualization is 30 characters. When qualified with : and the skill name, the combined names push past the 64-char threshold:

| Qualified name | Length |
|---|---|
| build-web-data-visualization:grammar-of-graphics-and-declarative-visualization | 78 |
| build-web-data-visualization:scrollytelling-and-parallax-data-visualization | 75 |
| build-web-data-visualization:uml-and-software-architecture-visualization | 72 |
| build-web-data-visualization:typescript-data-visualization-engineering | 70 |
| build-web-data-visualization:statistical-and-uncertainty-visualization | 70 |
| build-web-data-visualization:geospatial-and-cartographic-visualization | 70 |
| build-web-data-visualization:accessibility-and-inclusive-visualization | 70 |
| build-web-data-visualization:dashboards-and-real-time-visualization | 67 |

The 10 other skills in the same plugin have qualified names ≤ 64 and load fine.

Impact

Users lose access to 8 visualization skills (accessibility, dashboards, geospatial, grammar-of-graphics, scrollytelling, statistical, typescript-engineering, UML) with no actionable guidance — the warning references the SKILL.md path but not which field or what the computed name is.

Possible approaches

1. Raise the limit to at least 96 characters to accommodate compound plugin+skill names.
2. Only validate the skill-local name (from the SKILL.md name field) and let the qualified form be an internal composite.
3. Truncate or hash long qualified names internally instead of rejecting them.
4. Improve the warning to show the computed qualified name and the current limit so users can act on it.