perf(runtime): install agent script once per document

[yashranaway]

Closes #27

Summary

• extract the shared agent JavaScript into a compiled SwiftPM resource
• install it once per document in WebKit’s named content world
• preinstall it in Chromium, cache the isolated context, invalidate it from navigation/runtime events, and retry one stale-context race
• package and install the resource bundle on macOS, Linux tarballs, and Docker
• remove the jsdom regex extraction coupling and improve Linux E2E failure output
• mark backlog B7 and architecture decision 10 implemented

Validation

• npx --yes pnpm@9.15.0 test:runtime
• npx --yes pnpm@9.15.0 test:e2e:linux (includes 43/43 protocol tests and installed-resource coverage)
• shell syntax checks for build/install/E2E scripts