Clean up build warnings across Lite, Dashboard, and Installer

[erikdarlingdata]

Background

A full rebuild of Lite produces 190 unique warnings (380 raw — each fires twice because WPF compiles XAML through a temp project). Counts for Dashboard and Installer haven't been audited yet but likely have similar profiles.

Lite breakdown

Code	Unique count	Description	Verdict
CA1873	184	""Evaluation of this argument may be expensive and unnecessary if logging is disabled"" — fires on every _logger?.LogXxx(""…"", someField) call	Noise. The analyzer flags any non-literal argument. Real fix is LoggerMessage.Define source generators (big refactor) or if (_logger.IsEnabled(level)) wrappers (ugly). Suppress globally — the ""expense"" of a field access is negligible.
CS8604	2	""Possible null reference argument"" at Lite/Controls/CorrelatedTimelineLanesControl.xaml.cs:178,182 — passing a nullable collection to .Select(...)	Real. Fix with null-coalesce or guard.
CA1859	1	""Change return type from object? to Dictionary<string, object>? for performance"" at Lite/Mcp/McpAnalysisTools.cs:843	Real. Concrete return type avoids boxing.

Proposed approach

1. Add a project-root .editorconfig (or extend an existing one) that suppresses CA1873 with a justification comment.
2. Fix the three real warnings in Lite (CS8604 ×2, CA1859 ×1).
3. Run the same audit on Dashboard and Installer; fix what's real, suppress what isn't.
4. Verify dotnet build reports 0 warnings on all three projects.

Suppression should be global via .editorconfig, not per-file #pragma warning disable, so future code stays clean.

Out of scope

• Migrating to LoggerMessage.Define / source-generator logging (separate, larger effort).
• Treating warnings as errors. We can revisit TreatWarningsAsErrors once the count is at zero.

[erikdarlingdata]

Resolved by #948 — Lite 190→0, Dashboard 3→0, Installer was already 0. .editorconfig at repo root suppresses CA1873 with rationale; six real warnings fixed (2× CS8604 in Lite, 1× CA1859 in Lite, 3× CA1806 in Dashboard). Available in next nightly.