docs(KIM): correct susceptibility index comments

[marjohma]

Closes #264

Summary

• remove false I11 = I02 and I13 = I22 susceptibility identities from KIM comments
• explain that direct output/source power counting requires I11 and I13 for the j-B row
• state accurately that the I02/I22 pair printed in thesis equation 14.6 is incorrect
• update the matching characterization-test comment; executable formulas and test logic are unchanged
• include no external derivation/documentation files

Verification

• exhaustive KIM Fortran search finds no remaining false equality or transposition claim
• test_flr2_fourier_kernel passes after the commit
• independent re-review reported no findings