fix: standardize compound modifier hyphenation in README

[Copilot]

Fixes inconsistent hyphenation of compound modifiers in table descriptions:

• Changed "sub agent prompts" → "sub-agent prompts" (line 223)
• Changed "OpenAI API compatible" → "OpenAI API-compatible" (line 241)

Maintains consistency with technical documentation standards where compound adjectives modifying nouns require hyphenation.

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