test(api): register the master-route test hook as not host API

`setForceMasterPlaylistForTesting` is public for the same reason
`setForceSoftwarePathForTesting` is, so it belongs in the same list. Without
the entry the documentation-coverage test failed while every swift-testing
suite passed, which is a shape worth naming: `swift test` runs the XCTest half
and the swift-testing half in one process and prints the swift-testing summary
LAST, so a green summary line can sit under a red run. The exit code is the
only thing that says so.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WbciAqCSxpaiUpTumrCuA9

Author: superuser404notfound

Tests/AetherEngineTests/PublicAPIDocumentationTests.swift

@@ -58,6 +58,7 @@ final class PublicAPIDocumentationTests: XCTestCase {
     /// reading the docs is better off not meeting this symbol, so it carries its reason.
     private static let notHostAPI: [String: String] = [
         "setForceSoftwarePathForTesting": "test hook, aetherctl live --sw",
+        "setForceMasterPlaylistForTesting": "test hook, aetherctl live --force-master",
         "setSourceThrottleKbpsForTesting": "test hook, aetherctl --throttle-kbps",
         "setSoftwareBackgroundAudioOnlyForTesting": "test hook",
         "softwareVideoFramesEnqueuedForTesting": "test hook",