Add AC frequency sweep analysis (Bode plot) for filter circuits

[amaydixit11]

The simulator has AC analysis at a single frequency (MNASolver.solveAC(frequency)) but no frequency sweep capability.

Use Case

Students studying active filters (already in templates: active_filters.js) need to see how gain and phase vary with frequency.

Proposed Features

• A frequency sweep from f_start to f_stop with N points
• Bode plot: magnitude (dB) vs frequency and phase vs frequency
• Logarithmic frequency axis
• Export sweep data as CSV

Technical Approach

• Loop over np.logspace(log10(f_start), log10(f_stop), N) in JS
• Call solveAC(freq) for each point
• Collect results and plot on a chart
• The SimpleChart.js and OscilloscopeChart.js UI can be adapted for Bode plots