Debug mode: debug.slowMoMs and debug.highlight for live triage

Problem

Neither slowMo nor highlight exist anywhere in source today (grep -rn "slowMo\|highlight" src/main/java returns nothing). TraceRecorder (src/main/java/com/seleniumboot/tracing/TraceRecorder.java) and RecordingManager produce post-mortem artifacts (trace HTML, screenshots) after a test finishes, but there's no way to watch a test execute slowly or see which element the framework resolved in real time while it's still running.

Why it matters

Diagnosing a flaky locator or timing issue currently means re-running the whole suite and reading a static trace afterward, rather than watching the browser as it happens.

Proposed API

// SeleniumBootConfig — new Debug section
public static final class Debug {
    private long slowMoMs = 0;       // delay after each terminal action
    private boolean highlight = false; // JS outline on the resolved element before acting
    // getters/setters
}

debug:
  slowMoMs: 300
  highlight: true

// Locator.java — applied in resolve() / terminal actions, e.g. click()
public void click() {
    WebElement el = waitForClickable(resolve());
    DebugSupport.highlightIfEnabled(driver(), el);
    el.click();
    DebugSupport.slowMoIfEnabled();
}

Acceptance criteria

• debug.slowMoMs and debug.highlight config keys added
• Highlight applies a temporary JS outline (e.g. outline: 2px solid red) to the resolved element immediately before each terminal action in Locator, restored/left as-is after (define which)
• slowMoMs sleeps for the configured duration after each terminal action
• Both are opt-in and no-op with zero overhead when unset/disabled (don't slow down default runs)
• Unit tests for the config plumbing; document that this is unsuitable for CI (dev-only)
• Docs note this complements TraceRecorder/RecordingManager — this is live triage, those are post-mortem

Start by reading SeleniumBootConfig and Locator, then review TraceRecorder and RecordingManager to understand the existing debugging flow. Identify terminal actions in Locator and the config-test structure before deciding how highlight restoration and slow-motion timing should work. Done means both keys are opt-in, covered by unit tests, documented as dev-only live triage, and do not affect default runs.