WPT test harness and initial DOM pass rate #286

Implements issue 3mhyfpshyza2n

Summary #

• Adds a WPT (Web Platform Tests) test runner as a cargo test integration test
• Implements a testharness.js JavaScript shim providing test(), async_test(), promise_test(), and all standard assert_* functions
• Includes 16 embedded WPT-style HTML test files covering:
  • dom/nodes/ — createElement, appendChild, removeChild, insertBefore, replaceChild, cloneNode, textContent, getElementById, getAttribute/setAttribute
  • dom/events/ — addEventListener, dispatchEvent, removeEventListener, event bubbling
  • dom/collections/ — getElementsByTagName
  • html/dom/ — document properties (documentElement, body, head), querySelector/querySelectorAll
  • console/ — console.log, console.error, console.warn
• Test runner features: panic isolation via catch_unwind, instruction-count timeouts, results grouped by directory, silent panic hook
• Initial pass rate: 48/48 subtests passing (100%)

Test plan #

• cargo fmt --all --check passes
• cargo clippy --workspace -- -D warnings passes
• cargo test --workspace passes
• cargo test -p we-browser --test wpt -- --nocapture shows grouped results