Migrate: Phase P2.14 prop interpolation codemod

[dbanksdesign]

Summary

• Convert styled-components prop interpolations (${props => props.color}, ${(props) => props.width}px, etc.) to createVar + assignVars + styles.class instead of skipping them
• Strip migrated props from JSX call sites and wire values through assignVars (including CSS suffixes like px)
• Still warn and skip unsupported patterns: theme access, conditionals, exported components, and non-JSX references

Test plan

• pnpm --filter @typestyles/migrate test (50 tests)
• Run npx typestyles-migrate src --write on a styled-components codebase with prop interpolations and verify output
• Confirm conditional/theme interpolations still emit warnings without changing files

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