Validate normalization builtin pattern preconditions

[ctoth]

Problem

Normalization builtin handlers still use non-null assertions for step.pattern, so handler preconditions live implicitly in TypeScript rather than in the YAML pipeline validator.

Evidence

• src/g2p/text-normalize.ts has seven new RegExp(step.pattern!, step.flags) calls in builtin handlers.
• validateNormalizationPipelineConfig() currently checks known builtin handler names, but does not require the pattern field for handlers that need one.
• The YAML pipeline depends on those patterns for dateToWords, isoDateToWords, timeToWords, currencyToWords, decimalToWords, ordinalToWordsInline, and numberToWordsInline.

Acceptance criteria

• Remove step.pattern! from src/g2p/text-normalize.ts.
• Validate handler-specific requirements at pipeline load time: pattern-required handlers must define a string pattern, and patternless handlers must not silently rely on undefined state.
• Add focused tests for at least one missing-pattern builtin and one valid patternless builtin (lowercase or punctuationCleanup).
• Errors use E_NORMALIZE_CONFIG.
• npm.cmd run typecheck:core passes.