fix(368): remediate nullable-reference debt in SVGControl/ via per-file opt-in

[drmoisan]

Summary

• Remediates pre-existing nullable-reference-type debt (CS86xx) in the 12 hand-authored .cs files under SVGControl/ (a separate net481 WinForms control project, WinForms controls + SVG parser/renderer/selector + type converters/editors) using a per-file #nullable enable opt-in. No project-level or solution-level <Nullable> element is introduced; SVGControl.csproj retains no <Nullable> element.
• Annotation and null-safety only: nullable annotations (?), null guards, justified null-forgiving operators (!), and flow-narrowed locals. No behavior changes, no refactors, no renames/deletions of dead code (SvgOptionsConverter1, unreferenced SVGParser.cs), no API redesign.
• Fixes an incidental Set-StrictMode scalar/array-coercion bug in the shared scripts/vscode/Invoke-MSTestWithCoverage.ps1 test-assembly discovery pipeline (wraps the Get-ChildItem pipeline result in @(...)), discovered while capturing this feature's own coverage evidence.
• This is Wave-0 child issue Feature: utilitiescs-nullable-svgcontrol #368 of the utilitiescs-nullable-remediation epic. Base branch is the epic integration branch, not main.

Verification

• dotnet tool run csharpier check . — clean.
• msbuild TaskMaster.sln /t:Rebuild /p:Configuration=Debug /p:Platform="Any CPU" /p:TreatWarningsAsErrors=true (the per-file pragma gate, solution-wide, without /p:Nullable=enable) — zero CS8xxx diagnostics anywhere in the solution. Six pre-existing, unrelated errors remain (CS0649 x2 in SvgImageSelector.cs, CS0006 x4 in VBFunctions.csproj), confirmed present at this feature's own Phase 0 baseline and reproduced independently by the reviewer and by the orchestrator.
• pwsh scripts/vscode/Invoke-MSTestWithCoverage.ps1 — 37/37 tests passed; RelativePath.cs (the one file with a pre-existing automated baseline) shows byte-identical coverage before/after (56.75% line / 54.35% branch).
• No <Nullable> element exists in SVGControl.csproj or at the solution level (AC2), independently reverified.

Acceptance Criteria (issue #368)

All 6 acceptance criteria (AC1-AC6) are checked off in docs/features/active/utilitiescs-nullable-svgcontrol/issue.md and were independently re-verified by feature-review (not merely re-read): zero CS86xx under the per-file pragma, no project/solution <Nullable> element, no behavior change, no coverage regression, behavior-compatible public signatures, and Designer/generated files left untouched or only mechanically edited.

Known, accepted, out-of-scope findings (not introduced by this feature)

Feature-review flagged two procedural findings, both dispositioned in
docs/features/active/utilitiescs-nullable-svgcontrol/coverage-artifact-disposition.2026-07-19T12-00.md
as known, accepted, out-of-feature-scope gaps, consistent with documented repository precedent
(issue #309 / PR #311, merged 2026-07-11 with an identical finding unresolved):

1. Canonical artifacts/csharp/coverage.xml / artifacts/pester/powershell-coverage.xml absence. Independently reproduced: a plain msbuild TaskMaster.sln /t:Build fails CS0006 for UtilitiesCS.csproj/VBFunctions.csproj due to a pre-existing packages.config analyzer-version-pin mismatch, unrelated to SVGControl/ and unrelated to the already-fixed Moq/binding-redirect issue (Bug: stale-app-config-binding-redirects #354/PR Fix stale app.config binding redirects across the solution #359, already merged into this branch). This blocks generation of a genuine repo-wide C# coverage artifact in this environment; not introduced or worsened by this feature.
2. Missing regression test for the incidental PowerShell fix. The Invoke-MSTestWithCoverage.ps1 array-wrap fix was independently re-verified functionally correct by rebuilding and re-running the affected code path; a follow-up extraction + Pester test is recommended but not merge-blocking (tracked in the disposition doc).

Evidence

Full baseline, per-batch, and final-QC evidence lives under
docs/features/active/utilitiescs-nullable-svgcontrol/evidence/{baseline,qa-gates,regression-testing,other}/.
Review artifacts: policy-audit.2026-07-19T11-15.md, code-review.2026-07-19T11-15.md,
feature-audit.2026-07-19T11-15.md, remediation-inputs.2026-07-19T11-15.md.