fix(SKILL.md): quote argument-hint so YAML parses it as string

[thejesh23]

Summary

SKILL.md has:

argument-hint: [ex-name-or-slug]

In YAML, an unquoted [...] value is a flow sequence (an array), not a string. Copilot CLI 1.0.65 requires argument-hint to be a string, so loading the skill currently fails validation on that runtime.

The fix quotes the value so YAML parses it as a string while preserving the visible [ex-name-or-slug] hint that users see:

argument-hint: "[ex-name-or-slug]"

Verified locally with yaml.safe_load — the value now parses as str '[ex-name-or-slug]' instead of list ['ex-name-or-slug']. Claude Code has been tolerant of the array form, but the same latent inconsistency has been reported there too (see refs below).

YAML rule

• argument-hint: [X] → sequence [X] (WRONG for tools expecting a string)
• argument-hint: "[X]" → string "[X]" (CORRECT)
• argument-hint: ["X"] → sequence ["X"] (WRONG)
• argument-hint: "X" → string "X" (CORRECT)

Scope

Full-tree scan for argument-hint: in this repo turned up exactly one occurrence — SKILL.md line 4. The generated per-ex SKILL.md template embedded in this file (Step 5) does not emit an argument-hint field, so no other changes are needed.

References

• Latent report against Claude Code: [BUG] argument-hint YAML frontmatter with brackets causes React error #31 and unrecoverable TUI hang anthropics/claude-code#22161

Test plan

• yaml.safe_load on the updated frontmatter returns argument-hint as str
• Load create-ex skill in Copilot CLI 1.0.65 and confirm the frontmatter validates
• Load create-ex skill in Claude Code and confirm the [ex-name-or-slug] hint still renders as before

[thejesh23]

Tracking issue: #81 — captures the bug diagnosis and reproducer separately for anyone searching the repo who lands there before this PR.