Adds symbolic epoch tags to every cycle entry:
⟳WW.D:NNN
⟳ turnover glyph
WW ISO week-of-year (01-53)
D ISO weekday (1=Mon ... 7=Sun)
NNN daily cycle counter, resets at midnight UTC
Raw cycle integer preserved for backward compat. New fields:
epoch, epoch_week, epoch_weekday, epoch_daily_n in cycles.jsonl.
Summary gains current_epoch, by_week, by_weekday distributions.
loop_introspect.py prints current epoch in header output.
Daily counter persists in .loop/retro/.epoch_counter and
resets on date rollover (day turnover) while week number
advances per ISO calendar (week turnover).
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