Add Elzerman readout illustration

[kiro-agent]

This pull request was created by @kiro-agent on behalf of @VanOschB 👻

Comment with /kiro fix to address specific feedback or /kiro all to address everything.
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Summary

• Adds a simple 1200×700 energy-selective Elzerman spin-readout illustration as a PNG.
• Adds the editable SVG source.
• Shows the spin-up tunnel-out/reload sequence and sensor pulse alongside the spin-down blocked sequence and flat trace.

Verification

• Visually inspected the rendered PNG against the existing figure style.
• Confirmed the alignment condition E_down < μ_R < E_up.
• Confirmed six dot/reservoir snapshots, Γ_out and Γ_in transitions, and pulse/flat I_CS traces.
• Confirmed PNG dimensions and matching SVG viewBox.

Limitations

• None.