Add structure-group conformational comparison

[CedricHermansBIT]

Adds residue-level comparison of biologically defined structure sets such as apo/holo, WT/mutant or experimental/predicted groups.

Highlights:

• globally sequence-aligns every uploaded structure to one selected reference chain and automatically chooses the best matching protein chain per file;
• exposes and exports chain-selection quality (identity, reference coverage, candidate coverage and aligned residues);
• reuses RamplotR's circular ensemble statistics for per-group phi/psi means and SDs;
• calculates wrapped between-group delta-phi/delta-psi and a transparent combined backbone-displacement effect size for residue navigation;
• marks low-dispersion >=30-degree shifts only when both groups contain at least two observations and max within-group circular SD is <=15 degrees;
• tracks modal Rama8000 category changes independently from angular shifts;
• adds an interactive residue track and detailed table, linked back to the main residue inspector;
• exports both residue-level results and matched structure/chain metadata;
• makes no statistical-significance or dynamics claim; thresholds are explicitly navigation aids.

Tests cover chain matching, circular wraparound, group effect calculations and an end-to-end identical-1CRN-vs-1CRN browser comparison that must not invent a shift.