Consolidate ChatService reconciliation and fix live IM replay

Merge archives, plaintext and head previews by service ID and occurrence
before applying history limits. Keep loaded history and visible context in
ChatService so IM sessions and previews share one composer, with ordinary
live appends remaining independent of history replay.

Preserve original bodies and send-versus-receipt timing through offline
delivery and translation. Match known send times exactly and online receipt
times within a rolling 60-second window. Consume eligible occurrences once
in chronological order so repeated messages survive reconciliation across
minute boundaries.

Link offer fallback text to its notification ID and advance the replay
cursor for each actual row. Missing or delayed fallback rows can no longer
cause the following live IM to be skipped.

Dispatch ChatService presentation through the main-loop queue with runtime
and current-state checks. This prevents login deadlocks from reentering
font initialization in another coroutine. Await deletion invalidation
before continuing cleanup so a delayed clear cannot erase later messages.

Validated with the Release viewer build, all 34 LLChatServiceHistoryCore
cases, and native delivery, archive, offer replay and coroutine-deadlock
fixtures. The deadlock fixtures reproduce the original hangs and pass with
deferred presentation.

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