Add standalone prediction ensemble reporting

[CedricHermansBIT]

Stacked on the prediction-ensemble PR.

Adds a self-contained HTML research report for prediction ensembles:

• ensemble overview metrics;
• explicit interpretation warning that model spread is prediction uncertainty/heterogeneity, not experimental dynamics;
• model-level provenance including labels and coordinate hashes;
• the 25 largest local backbone-variability positions ranked by max circular SD(phi, psi);
• full residue-level phi/psi, Rama8000 and pLDDT ensemble statistics;
• analysis provenance and reference settings;
• direct download from the Summary ensemble workflow.

Includes report-generation regression coverage and documentation.