Replace per-case trackers with a unified key-based tracker and tighten detection logic. Introduces buildMessageTrackingKeys/collectTrackableText to canonicalize text, extract invite codes, include image fingerprints and dedupe keys; replaces trackCrossChannelMessage/trackImageOnlySpam with trackCrossChannelKeys that tracks multiple normalized keys. Simplifies detectSpam to use trackable content and invite-aware link handling, updates message preview/attachment embedding, and adjusts command/help text to reflect the new "same content across channels" rule. Overall reduces duplicate-prior merging and streamlines cross-channel spam handling.