export default function() {} and export default class {} are valid
JavaScript but the parser incorrectly required a name. Check whether
the function/class has a name and route to expression parsing when
anonymous.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Add a recursive-descent JavaScript parser with Pratt expression parsing
for ECMAScript 2024. Transforms the token stream from the lexer into an
Abstract Syntax Tree.

AST node types cover:
- All expression types (literals, binary, unary, assignment, member access,
call, new, arrow functions, template literals, spread, yield, await)
- All statement types (if, for/for-in/for-of, while, do-while, switch,
try/catch/finally, return, throw, break, continue, labeled, with)
- Variable declarations (var/let/const) with destructuring patterns
- Function declarations (sync, async, generators)
- Class declarations (constructor, methods, getters/setters, static)
- Import/export declarations (default, named, namespace, re-export)

Features:
- Operator precedence via Pratt parsing with binding power table
- Automatic Semicolon Insertion (ASI) using lexer newline tracking
- Arrow function detection with expression-to-pattern reinterpretation
- Destructuring patterns (array, object, default values, rest)
- for-in/for-of disambiguation with allow_in flag
- 73 unit tests covering all grammar productions and error cases

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>