Add the fetch interception pipeline for controlled clients.
Scope:
- During document navigation and subresource loading, find the longest-matching active service worker registration for the request URL origin/scope.
- Construct Request objects for intercepted document, CSS, script, image, and fetch() requests.
- Dispatch FetchEvent to the active worker and use respondWith() Response values as the browser response.
- Support network fallback when no worker controls the request or when the worker deliberately falls through.
- Propagate redirects, cancellation, body stream errors, and network failures consistently.
Acceptance criteria:
- Tests cover scope matching, controlled vs uncontrolled clients, synthetic HTML responses, subresource interception, and network fallback.
- Existing loader behavior is unchanged when no service worker registration matches.
- Add or extend e2e coverage for a page whose worker intercepts a navigation and a subresource.