Unattended capture of an Article always warns that the conversation never mounted #64

Impact: every unattended capture of an X Article returns the warning only the root post was captured; the conversation never mounted (settled on 0 post(s) after 0ms). Articles never run waitForConversation, so the result reports untouched diagnostics. A caller that treats warnings as failures rejects every Article. The diagnostics object is also never reset between captures, so counters from an earlier capture can leak into a later result.

Where: runAutomatedShareCapture in sourcecapsule.user.js copies conversationWaitDiagnostics (~5800) and passes it to singlePostCaptureWarning (5723), which warns whenever settled <= 1.

Evidence: Node repro of the Article path:

diagnostics as an article capture sees them: {"ran":false,"startedWith":0,"settled":0,"sameAuthor":null,"elapsedMs":0,"timedOut":false}
warning pushed for a 1-document article: "only the root post was captured; the conversation never mounted (settled on 0 post(s) after 0ms)"

Same family as #50 (closed), which fixed the false warning for single posts with replies.

Environment: main 72777ef (v1.6.8). Engine loaded in Node through the module.exports guard. No browser.

Next action: skip the scope warning when the model is an Article or when conversation.ran is false, and reset the diagnostics at the start of each capture.