tstest/natlab/vmtest: add macOS VM screenshot streaming to web UI

When --vmtest-web is set, Host.app is launched with --screenshot-port 0
to start a localhost HTTP server that captures the VZVirtualMachineView
display. The Go test harness parses the SCREENSHOT_PORT=<port> line from
stdout, then polls every 2 seconds for JPEG thumbnails and pushes them
over WebSocket to the web dashboard.

Clicking a screenshot thumbnail opens a full-resolution image proxied
through the web UI's /screenshot/{node} endpoint.

Screenshot events are excluded from the EventBus history (they're large
and only the latest matters, stored in NodeStatus.Screenshot).

Updates #13038

Change-Id: I9bc67ddd1cc72948b33c555d4be3d8db06a41f6d
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

tstest/tailmac/Makefile

@@ -5,12 +5,12 @@ endif
 
 .PHONY: tailmac
 tailmac:
-	xcodebuild -scheme tailmac -destination 'platform=macOS,arch=arm64' -derivedDataPath build -configuration Release build | $(XCPRETTIFIER)
+	set -o pipefail && xcodebuild -scheme tailmac -destination 'platform=macOS,arch=arm64' -derivedDataPath build -configuration Release build | $(XCPRETTIFIER)
 	cp -r ./build/Build/Products/Release/tailmac ./bin/tailmac
 
 .PHONY: host
 host:
-	xcodebuild -scheme host -destination 'platform=macOS,arch=arm64'  -derivedDataPath build -configuration Release build | $(XCPRETTIFIER)
+	set -o pipefail && xcodebuild -scheme host -destination 'platform=macOS,arch=arm64'  -derivedDataPath build -configuration Release build | $(XCPRETTIFIER)
 	cp -r ./build/Build/Products/Release/Host.app ./bin/Host.app
 
 .PHONY: clean

tstest/tailmac/Swift/Host/HostCli.swift

@@ -202,12 +202,6 @@ class ScreenshotHTTPServer: NSObject {
         let n = read(fd, &buf, buf.count)
         let requestLine = n > 0 ? String(bytes: buf[..<n], encoding: .utf8) ?? "" : ""
 
-        // Route: POST /keypress?key=<keycode> — send a key event to the VM.
-        if requestLine.contains("/keypress") {
-            handleKeypress(fd, requestLine)
-            return
-        }
-
         // Route: GET /screenshot — capture the VM display.
         let wantFull = requestLine.contains("full=1")