Docs: rewire LQI load-disturbance example with advanced feedback interface

[baggepinnen]

Summary

Rewire the LQI load-disturbance example in docs/src/lqg_disturbance.md to use the named-system feedback(s1, s2; w1, u1, w2, u2, z1, z2, pos_feedback) interface, matching the style already used by the model-mismatch section that follows it on the same page.

Two features of the advanced interface make the wiring direct:

• Listing :u_plant in both w1 and u1 reuses the plant input as the summing point for the load disturbance — no augmented disturbance port on G is needed.
• Omitting :y_plant_r from both w2 and u2 silently grounds the reference (r = 0) without padding lsim inputs with a zero column. A commented # w2 = :y_plant_r line shows readers that exposing it externally is one keyword away.

Time response is numerically identical to the previous wiring (max |Δ| ≈ 5e-15 over the full 100-step trajectory). The existing in-block @test res.y[:, end] ≈ [0, -1] atol=1e-3 and the plot labels are preserved verbatim.

Test plan

• Side-by-side lsim comparison of old vs. new closed-loop on the same disturbance closure — identical to round-off
• @example LQG_DIST block builds in the Documenter pipeline (CI)

🤖 Generated with Claude Code

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.84%. Comparing base (b0b41fb) to head (0578c7f).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #150      +/-   ##
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+ Coverage   91.78%   91.84%   +0.06%     
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  Files          20       20              
  Lines        3067     3067              
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+ Hits         2815     2817       +2     
+ Misses        252      250       -2     

Flag	Coverage Δ
unittests	91.84% <ø> (+0.06%)	⬆️

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