fix: output files (.dat, SVG, exact parameters, Delta Cp)

[PSamuele]

What

• .dat files: one point per line. The first line is the airfoil name with the exact m, p, t (XFOIL reads it as the name).
• optimization_history.svg is now a real SVG (it was a PNG with an .svg extension).
• Exact m, p, t are printed at the end of the run and written in the aerodynamic CSV (the NACA name is rounded).
• Delta Cp: the lower-surface Cp is interpolated at the upper-surface x/c. Before, upper and lower points were paired by index, i.e. at different x/c (up to 0.29 difference near the LE on a NACA 2412 at 4 deg; zero on symmetric airfoils).
• README: output table updated, "Known issues" section removed.

Verified

• Baseline 24/24.
• .dat: 400 lines (name + 399 points), loaded by XFOIL.
• SVG files start with <?xml.
• XFOIL optimizer: same numbers as before, plus the new "Exact parameters" line.

Note

The "Global Coefficients" row of the aerodynamic CSV has 3 new columns (m, p, t).
The example folders already in Results/ were generated before this fix and still have the old problems.

Depends on

#5 (base branch: refactor/shared-core).