Make editor default to 1x speed

[x46085]

Note

Low Risk
Small, localized changes to default timing constants and initial stream state; low risk beyond potentially altering expected initial playback speed for existing DBs.

Overview
Makes editor playback always start at 1x real-time by standardizing the initial fixed-rate stream time_step to 1/60s at 60 Hz, regardless of what DbConfig.default_stream_time_step is stored in the DB.

Updates the DB default creation time-step from 1/120s to 1/60s, and clarifies in the server init logic that playback speed is a requester concern (while still persisting a computed default time-step).

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[chatgpt-codex-connector]

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