Fix strict documentation build prerequisites

[ChrisRackauckas-Claude]

Ignore this PR until reviewed by @ChrisRackauckas.

Summary

• remove Documenter warnonly so docs failures are fatal
• update rendered tutorial imports and Makie triplot! keywords for current dependencies
• expose the required LinearSolve import in the diffusion developer example
• declare SciMLOperators as a runtime dependency and import MatrixOperator from its owning module

This is a focused prerequisite for the strict SciMLTesting 2.4 public-API/documentation audit. The separate local Literate regeneration failure found on clean main is tracked in #131.

Root cause

A clean-main worker reproduced the ownership break on exact origin/main 0bb35b4:

• SciMLBase 3.39.1: isdefined(FiniteVolumeMethod, :MatrixOperator) passes
• SciMLBase 3.40.0: the same assertion fails
• SciMLBase commit 8e770b8d8a4bf0fc7d5c3d2909139fb275ab335d / SciMLBase#1476 intentionally removed the blanket SciMLOperators reexport

FiniteVolumeMethod therefore needs to depend on the module that owns this API instead of reaching it through SciMLBase.

Local validation

• CI=true julia +release --project=docs -e 'using Pkg; Pkg.develop(PackageSpec(path=pwd())); Pkg.instantiate(); include("docs/make.jl")': passed with fresh current dependencies (doctests, examples, checkdocs, cross-references, HTML render; exit 0)
• release owner-load assertion: passed
• Julia 1.10 owner-load assertion: passed
• Runic 1.7.0 check: passed
• git diff --check: passed

The clean-main non-CI regeneration failure was reproduced independently and is not silenced or allow-listed here.

[ChrisRackauckas-Claude]

Clean-main ownership investigation (exact origin/main 0bb35b4):

• With SciMLBase 3.39.1, isdefined(FiniteVolumeMethod, :MatrixOperator) passes.
• With SciMLBase 3.40.0, the same assertion fails because the imported binding is undefined.
• The boundary is SciMLBase commit 8e770b8d8a4bf0fc7d5c3d2909139fb275ab335d / SciMLBase#1476, which intentionally removed the blanket SciMLOperators reexport.

The focused follow-up commit therefore declares SciMLOperators as a runtime dependency and imports MatrixOperator from its owning module. Release and Julia 1.10 owner-load smoke checks pass locally; the strict docs build is running before the branch is updated.