Add the Console API as built-in JS globals (Phase 11, issue 1 of 8).

- ConsoleOutput trait with configurable output sink (default: stdout/stderr)
- console.log/info/debug write to the log channel
- console.error writes to the error channel
- console.warn writes to the warn channel
- Rich formatting: arrays show contents, objects show properties
- Cycle detection and depth limiting for nested structures
- Vm::set_console_output() for redirecting output (dev tools, testing)
- 14 tests covering all methods, formatting, and channel routing

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

- Remove stream-of-consciousness comments in async_resume_callback, replace
with concise doc explaining the actual mechanism
- Rename misleading test_async_arrow_* tests to test_async_function_expression*
(they tested function expressions, not arrows)
- Add real async arrow function tests using `async x => ...` syntax
- Add Executing state guard to throw_into_generator for consistency with
run_generator (prevents re-entrancy)

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

Add async/await support to the JavaScript engine:

- Add `Await` opcode (0x82) to bytecode format
- Add `is_async` flag to bytecode Function struct
- Compile async function declarations, expressions, arrows, and methods
- Compile `await expr` to emit Await opcode
- Parse `for await...of` syntax
- VM creates internal generator for async functions, driven by promises
- Await suspends generator and sets up promise reactions for resume
- Rejected await throws into generator (preserving try/catch)
- Save/restore exception handlers across yield/await suspension points
- Async generators return async iterator wrappers
- 16 unit tests covering all async patterns

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