Add 'What is a Gateway Server?' foundational explanation to Chapter 2 #11

Job	Run time
checks-windows (node, protocol, pnpm protocol:check)	1d 0h 0m 0s
checks-windows (node, build, pnpm build)	1s
checks-windows (node, test, pnpm test)	1d 0h 0m 0s
checks-windows (node, lint, pnpm lint)	1s
android (build, ./gradlew --no-daemon :app:assembleDebug)	1s
android (test, ./gradlew --no-daemon :app:testDebugUnitTest)	1s
checks (bun, test, bunx vitest run)	1s
checks (node, build, pnpm build)	1d 0h 0m 0s
checks (node, protocol, pnpm protocol:check)	1s
checks (node, lint, pnpm lint)	1s
checks (bun, build, bunx tsc -p tsconfig.json)	1s
checks (node, format, pnpm format)	1d 0h 0m 0s
secrets	1s
install-check	1d 0h 0m 0s
macos-app	0s
checks (node, test, pnpm test)	1s
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ios	0s
	5d 0h 0m 10s

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