fix(vo2max): rebalance rep-length conflict, correct overstatements

Review of the VO2 conflict section against primary sources (verified via
PubMed + search):

- Rønnestad & Hansen 2016 (PMID 23942167) confirmed: 13 cyclists, 30s vs
  50%/80% Tmax at 2:1 work:rest, measured time >=90% VO2peak, 30s won. Table
  row corrected to reflect the actual comparison.
- Yang 2025 optimum ~140s is a MEDIUM rep (~2.3 min), between the poles.
  Section reframed from binary short-vs-long to an inverted-U with a
  modality/protocol-dependent peak. 'Weighted toward running' softened to
  match what the abstract actually supports.
- Removed the overstatement 'best-controlled evidence favors short 30/15
  intervals'. Added two caveats: (1) cycling short-interval superiority is
  largely one research group; (2) effort-matched work (total-work-matched)
  reportedly nulls the advantage (Seiler group; unpublished/secondary,
  flagged low-tier, not cited as fact).
- Practical menu now defaults to medium (~2-4 min, near the pooled optimum)
  rather than short; short/long presented as goal-dependent options.
- citations.md: added single-group caveat on Ronnestad body of work and an
  explicit NOT-VERIFIABLE entry for the effort-matched replication.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TqrhBhC3GEcKyaw8RTk8G6

references/citations.md

@@ -152,6 +152,19 @@ Rønnestad BR, Øfsteng SJ, Zambolin F, Raastad T, Hammarström D. *Superior Phy
 After a Microcycle of Short Intervals Versus Long Intervals in Cyclists.* Int J Sports Physiol
 Perform. 2021;16(10):1432–1438. **PMID 33735833 · DOI 10.1123/ijspp.2020-0647.**
 
+> **Caveat on the cycling short-interval body of work (Rønnestad 2016/2020/2021 + Almquist 2020):**
+> the short-interval superiority comes chiefly from a **single research group**, and its adaptation
+> claims are challenged by effort-matched work: when **total work duration** is matched, the
+> advantage reportedly disappears (attributed to a Seiler-group study — **unpublished /
+> secondary-source, low evidence tier, not cited as fact**). Present short-interval superiority as a
+> *lab-consistent but not independently settled* finding, not a cycling consensus. See
+> `vo2max-intervals.md`.
+
+**❌ "Effort-matched cycling replication, no difference" (Seiler group)** — **NOT VERIFIABLE as a
+primary source.** Referenced only via secondary/coaching sources as an unpublished master's thesis
+(~30 cyclists, VO2max ~64, total-work-matched, no short-vs-long difference). Used only to *temper*
+overconfidence in the short-interval side; **do not cite as established evidence.**
+
 ---
 
 ## Distribution / periodization philosophy