feat: add native DOM hover highlight

[jevin98]

What changed

• Added a Chrome debugger/CDP overlay highlighter for DOM diff source/target hover rows.
• Captured selected DOM metadata, including inspect id, DOM path, and inspected tab id.
• Limited hover highlighting to DOM nodes selected in the current inspected tab.
• Prepared the debugger overlay after two local elements are selected, so the first hover is not interrupted by Chrome's debugging notice.
• Added localized tooltip copy and README documentation for the required Chrome debugger permission.
• Added unit coverage for inspected element resolution, debugger overlay behavior, stale hover cancellation, cross-tab filtering, and tooltip behavior.

Why

• Users need a direct way to map each source/target column in the CSS diff table back to the real DOM node on the inspected page.
• The diff table can show many CSS properties, and without page-side feedback it is easy to lose track of which page element each side represents.
• Native page highlighting makes the comparison workflow closer to Chrome's built-in element inspection interaction.

User impact

• Users can hover a DOM line or CSS value cell in the diff table and immediately see the corresponding DOM node highlighted in the inspected page.
• Users do not need to switch back to the Elements panel or reselect nodes just to confirm which element a diff column represents.
• Chrome may show a debugger permission warning or a browser-level debugging notice because the feature uses Chrome's debugger API.
• If the debugger permission is unavailable, CSS comparison still works, but native page hover highlighting is unavailable.

Developer impact

• The hover highlight path now uses CDP Overlay.highlightNode / Overlay.hideHighlight instead of mutating DevTools selection with inspect().
• Selected element data now carries inspect metadata used by the overlay highlighter.
• The debugger session is attached and enabled after local selections are ready, then detached on clear/remove/unmount.
• Tests cover the main overlay states and guard against stale async hover requests drawing an old highlight.

Root cause

• Not applicable. This is a feature PR.

Validation

• pnpm exec eslint . --fix
• pnpm test:unit
• pnpm compile
• pnpm exec wxt prepare
• pnpm build:chrome
• pnpm build:firefox
• pnpm build:edge
• After rebase onto origin/main: pnpm test:unit, pnpm compile, pnpm build:chrome