* [Client] Transient User Alts investigation tab
New TabAlts tab with user search, depth selector (1-3), and an alt table showing per-row match evidence (Via, Depth, Shared fan-out) alongside the account data. Sends Command_GetUserAlts with the requested depth and degrades gracefully against old servers (missing evidence fields render as dashes). Wired as a transient single-reuse tab via TabSupervisor::openTabAlts with no menu action or persisted setting; closed on disconnect like the other staff tabs.
* Fix remaining review threads on the user alts tab
- Switch to the User Alts tab when it is created, so the first investigate
click does not open it in the background.
- Treat an empty RespOk as "user not found" and use a generic message for
error codes, matching what the server actually returns.
- Exclude the depth-0 seed row from the related-account count.
- Guard the reply with the requested user name so a stale response cannot
overwrite a newer one.
- Move the duplicated formatEpoch body into widgets/utility/epoch_format.h.
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Co-authored-by: Lukas Brübach <Bruebach.Lukas@bdosecurity.de>
