Replace 'tabCapture' with 'desktopCapture' to match the new
getDisplayMedia capture path (D-A6). Remove 'alarms' because the
Phase 01 SW keepalive moves to a long-lived chrome.runtime.connect
port and the alarms code is deleted in Plan 05; declaring an unused
permission expands attack surface and is mitigated here per T-1-02.
activeTab is retained for chrome.tabs.captureVisibleTab in Phase 3,
and offscreen is retained for chrome.offscreen.createDocument.