Move the old chrome.debugger branching into separate class from new main loopback_cdp logic

[pirate]

Summary

• Add ServerUpstreamTransport with loopback CDP and chrome.debugger implementations behind one active server upstream interface.
• Add Mod.getTopology and extend AutoSessionRouter with target/session/context bookkeeping, frame topology, document roots, and pierced shadow root discovery.
• Add live Vitests for sdk -> ws -> service_worker -> loopback_cdp and sdk -> ws -> service_worker -> chrome_debugger routing.

Validation

• pnpm run typecheck
• pnpm exec vitest run js/test/test.AutoSessionRouter.ts js/test/test.ServerUpstreamTransport.ts --fileParallelism=false --maxWorkers=1

[pirate]

Superseded by #7 and #8. #7 contains the ServerUpstreamTransport / chrome.debugger split and related transport cleanup; #8 stacks on #7 with Mod.getTopology and the advanced AutoSessionRouter topology/session/context work. I verified the final stacked tree matches this PR head exactly.