README backend-selection snippet at README.md:39 is not runnable as shown #239

Subcategory: executable documentation
Current → target: 6 → 8

Problem

The "Linear solver backends" snippet at README.md:39 is not self-contained:

# Auto-detect best backend (default)
solver = scs.SCS(data, cone)

# Explicitly select a solver
solver = scs.SCS(data, cone, linear_solver=scs.LinearSolver.QDLDL)

It uses scs, data and cone, none of which are defined until the Usage fence at
README.md:85. Running the README's python fences in order fails:

README.md: python fences exited 1 — NameError: name 'scs' is not defined

(reproduced with check_doc_examples.py --source-root scs --run, executed in a venv with
the package built and installed, so this is not a missing-dependency artefact).

The Usage quickstart at README.md:85 itself is correct — verified in the same environment,
it prints status: solved and a populated aa_stats dict, and both
LinearSolver.QDLDL and LinearSolver.ACCELERATE solve successfully. Only the earlier
snippet is unrunnable as shown.

Files / lines to change

README.md:39 — either add the three lines that define data and cone (plus import scs),
or move the backend-selection fence after the Usage section.

Done when

Running the README's python fences in document order exits 0.