fix: quote the four remaining argument-hint values (follow-up to #69)

[Caho1]

Follow-up to #69, closes the remaining part of #68.

Summary

Four skills still carry an unquoted argument-hint: value whose text starts with <…> and contains [… : …]:

• skills/cheat-learn-from/SKILL.md
• skills/cheat-predict/SKILL.md
• skills/cheat-publish/SKILL.md
• skills/cheat-retro/SKILL.md

Same mechanical fix as #69: wrap the value in double quotes so every YAML parser reads it as a plain string.

- argument-hint: <script-path> [— mode: v1|v2] [— prediction-file: <path>] [— skip-blind]
+ argument-hint: "<script-path> [— mode: v1|v2] [— prediction-file: <path>] [— skip-blind]"

Why #69 missed these four

#69 was about values that start with [, which YAML parses as a flow sequence. These four start with <…>, so they look like plain scalars — but the : inside the bracketed part (way: a, mode: v1, platform: …, window: 3) reads as a nested mapping, which is a hard parse error rather than a shape mismatch. Lenient parsers (PyYAML safe_load) accept it, so a lint pass can miss it; strict parsers reject the whole frontmatter.

Impact

Strict loaders drop the skill entirely. With pi 0.85.1's skill loader, which uses the yaml package:

before -> skills: []                  diagnostics: ['Nested mappings are not allowed in compact mappings at line 3, column 16']
after  -> skills: ['cheat-predict']   diagnostics: 0

Verification

• Frontmatter of all 14 skills/*/SKILL.md plus the root SKILL.md parses with the yaml package; each changed file returns argument-hint as a str
• loadSkillsFromDir from pi 0.85.1 loads the changed skills with zero diagnostics (before: skill dropped + warning)
• No changed value contains " or \, so plain double-quote wrapping is safe and the parsed string is unchanged

The other unquoted hints (cheat-bump, cheat-score, cheat-score-blind, cheat-shoot) contain no : and parse as plain scalars, so they are left untouched.

Relation to #73

Same scope and same one-line change as #73, filed from a fork rebased on current main (d2d818f). Either one can be merged; happy to close this one if #73 lands first.