v2.1.0 release

Added

• 30/15s (Rønnestad) workout archetype in references/workout-library.md. Structure: 3 sets × 13 reps, 30 s @ 110–115% FTP / 15 s @ ~50–55%, 3 min recovery between sets. Includes cadence cues and a progression table (2×13 → 3×13 → 3×13 @ 112–115%).
• Progression row for 30/15s (Rønnestad) in the archetype progression table.

Changed

• Rotation table updated so 30/15s (Rønnestad) occupies the former VO2max slot for all rider types, backed by Rønnestad et al. research showing 3 × 13 reps produces significantly greater VO2max and power gains than 4–5 min evenly-paced intervals. Classic VO2max (4×4 min) is retained as an explicit fallback substitute.
• Example polarised week: Tuesday's session changed from VO2max 5×4 to 30/15s Rønnestad 3×13.