fix(skill): enforce skill name validation per documentation spec

[zerone0x]

What does this PR do?

Adds validation to skill names to match the documented requirements at https://opencode.ai/docs/skills/:

• 1-64 characters
• Lowercase alphanumeric with single hyphen separators
• Cannot start or end with -
• Cannot contain consecutive --
• Must match the directory name containing SKILL.md

Also adds:

• Description length validation (1-1024 characters)
• Logging of validation errors (previously skills with invalid frontmatter were silently skipped)

This addresses the maintainer's comment on #9294 requesting that the code be updated to match the documentation spec, rather than updating the docs to match the code.

Fixes #9294

How did you verify your code works?

• Added 3 new tests:
  • validates skill name format - Tests the NAME_REGEX against valid/invalid patterns
  • skips skills with invalid name format - Integration test for invalid skill names
  • skips skills where name doesn't match directory - Integration test for name/directory mismatch
• Existing tests all use valid skill names that match the regex and their directories

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[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Based on my search, I found one potentially related PR:

PR #9295 - docs: clarify skill naming is convention, not enforced
#9295

This appears to be directly related as it addresses the opposite approach - updating documentation to clarify that skill naming is a convention rather than enforced. Since your PR #9566 is implementing enforcement of skill name validation (per the maintainer's comment on #9294), PR #9295 represents the alternative approach that was apparently considered. You may want to check if #9295 is still open or if it's been addressed differently.

[yacinehmito]

This was purposefully removed by @thdxr. I see no reason to reintroduce that logic, it seems completely arbitrary. I think the docs should be fixed, not the code.