Defer hover tracking and test selector behavior

[jdalton]

Changes

• Install hover listeners only when a hover selector is compiled. Repeated queries reuse the listeners.
• Move the 46 Node tests into the existing unit and integration suites. Move the four browser tests into the existing e2e suite.
• Remove the separate regression runners and stale PR-history document.
• Update against current master without dropping either branch history.

Validation

• Node: 540 passed, two existing expected failures, ten skipped browser tests.
• Browser: 20 passed, two existing expected failures.
• WPT: 54 passed.
• Type checking and lint passed.
• Combined coverage: 84.22% statements, 75.70% branches, 83.16% functions, and 82.97% lines. Thresholds are unchanged.