Add TransformStream resource fallback

[wieslawsoltes]

Problem

The lower CacheStorage/request-broker entry can return complete Response bodies, but unchanged Code OSS also uses its Safari-style chunk fallback when a transferable stream is unavailable: new TransformStream(), writable.getWriter(), ordered write() calls, close()/abort(), writer.closed, and the readable side as the response body.

Result

• Adds browser-shaped WritableStream, WritableStreamDefaultWriter, and TransformStream brands, receiver checks, descriptors, locking, ordered writes, close, abort, ready/closed promises, and readable byte delivery.
• Keeps the enlarged fetch bootstrap in four MSVC-safe 9.0-9.6 KiB literals while preserving the concatenated snapshot source.
• Extends the lower 100-cycle broker test through the exact chunk fallback shape and adds a cumulative WPT-derived Chrome/native contract.

Part of #266. This cumulative entry merged after lower #303. The issue remains open for parser/image/style request interception, 200/206/304/range validators, security roots, and exact unchanged Markdown rendering.

Cumulative validation

• Clean snapshot/native build.
• Portable bootstrap literal regression: 2/2.
• Native service-worker-resource-plane: 100 cycles, p95 0.284 ms; V8 heap 1,161,272 -> 1,161,272 bytes; peak RSS 38,207,488 -> 49,430,528 bytes; oversized responses reject at 64 MiB before combined allocation.
• Native candidate contract: 1/1 document, 3/3 subtests, 67 ms after the bounded-body follow-up.
• Google Chrome 153 oracle: 1/1 document, 3/3 subtests, 138 ms.
• No lingering isolated Chrome process after the oracle run.
• Rebased head c6c26649 is conflict-free atop lower head bd1b872e and main 3d143240; the only Implement effective CSS property cascade semantics #305 path overlap is the additive component-profile ledger. Focused cumulative revalidation passes bootstrap/syntax/build, the native contract (3/3, 69 ms), and 100 cycles (p95 0.210 ms; heap 1,161,232 -> 1,161,232 bytes; peak RSS 38,207,488 -> 49,266,688 bytes). Evidence: /private/tmp/webscene-266-rebased-top-native-profile-3d143240/results.json.