Add a Web Platform Tests runner that discovers HTML test files, executes inline scripts with a testharness.js shim, and reports pass/fail/skip counts grouped by test directory. Includes: - testharness.js preamble: test(), async_test(), promise_test(), assert_equals, assert_true, assert_false, assert_not_equals, assert_throws_js, assert_throws_dom, assert_array_equals - Test runner with panic isolation and instruction-count timeouts - Results collection via tab-separated serialization from the VM - 16 embedded WPT-style HTML test files covering dom/nodes, dom/events, dom/collections, html/dom, and console APIs - Initial pass rate: 48/48 subtests passing (100%) Run with: cargo test -p we-browser --test wpt -- --nocapture Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>