♻️ Replace miette and owo-colors with codespan-reporting

[timfennis]

Summary

• Replace miette with codespan-reporting for error diagnostics
• Replace owo-colors with yansi (already a workspace dependency) for syntax highlighting
• Use codespan's .with_code() for error phase labels (e.g. error[lexer], error[vm])
• Convert InterpreterError directly to codespan Diagnostic, removing the intermediate NdcReport / Report struct
• Fix disassemble error path to pass source code through so span labels render correctly
• Document branch naming convention in CLAUDE.md

Test plan

• All 267 tests pass
• Clippy clean
• cargo fmt applied
• Manual check: run a script with an error and verify the diagnostic renders correctly
• Manual check: REPL error rendering
• Manual check: ndc highlight subcommand

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