Analyze ECS quotients on FC1 and FC2

[charlesmartin14]

Summary

• compute both exact ECS quotient covers for FC1 and FC2 in the reduced command-line runner
• make resume backfill missing FC2 spectra by checking the expected method set
• fail visibly when requested ECS rank prerequisites are unavailable
• add an explicit method-coverage CSV and HTML audit
• add a dedicated FC1/FC2 ECS plot with display-only marker offsets for coincident curves
• document the operators, spectral observation units, FC3 scope, and overlap semantics

Validation

• Python compilation passed
• shell syntax passed
• direct FC1/FC2/FC3 coverage contract passed
• synthetic ECS plot and HTML report generation passed
• git diff checks passed
• pytest unavailable in the validation environment