SUCCESS

All tuple pattern parser bugs fixed. All 4 test files transpile successfully:
- pattern_match_09_tuple_pairs.dingo ✅
- pattern_match_10_tuple_triples.dingo ✅
- pattern_match_11_tuple_wildcards.dingo ✅
- pattern_match_12_tuple_exhaustiveness.dingo ✅

Root cause: Parser was splitting expressions on commas inside string literals.
Solution: Implemented findExpressionEnd() that respects strings, nesting, and escapes.
Files modified: 1 (pkg/preprocessor/rust_match.go)
Functions updated: parseArms(), parseTupleArms()
New helper added: findExpressionEnd()

Edge cases handled:
- Nested patterns: (Ok(x), Ok(y)) ✅
- Wildcards: (_, Err(e)) ✅
- N-tuples: 2, 3-element tuples ✅
- String commas: "x, y" ✅
- Escaped quotes: "\"hello\"" ✅
- Backticks: `template ${x}` ✅
- Nested calls: foo(bar(x, y)) ✅

Zero regressions. All tests pass.
