R11: indoor track 2026-10-08 (walk/jog/run intervals); sessions.csv + README table to 11 sessions (part 2)

run 10, reports 08-10 + all reports (review), sync mode names BEACON_TIMESYNC / RECEIVER_TIMESTAMP

Drop second_phone column; phone_model for R01-R06 (Galaxy S24, reported); trim notes; new card blurb

Rename run/ to level/; meta-debug values into session_context; sensor voltage/temp; integer Polar ns; analysis figures

LEVEL Running Dataset: sessions R01-R09 (data + figures)