Fix Linux chart rendering and close four documentation loose ends in Logging

[FreeAndNil]

Render chart text on Linux

build/build.csproj referenced SkiaSharp.NativeAssets.Linux.NoDependencies,
which ships Skia without fontconfig. SKTypeface.FromFamilyName("Arial") in
build/Targets/TextStyle.cs therefore resolved to nothing on Linux, and
dotnet run --project ./build -- readme wrote all 132 charts with no text at
all: no title, no library names, no values. Switching to
SkiaSharp.NativeAssets.Linux pulls in fontconfig, which maps Arial to the
metric-compatible Liberation Sans.

Anyone regenerating charts on Linux today silently produces unusable PNGs, so
this is worth landing on its own regardless of the rest.

Logging documentation

Three findings, all in the Logging category:

1. workflows/feature-contracts/logging.md documented features 1-8 only.
   FormattedOutput was added as feature 9 and never written up. Added section
   9, sourced from the [MatrixFeature] and [FeatureUnavailable] attributes
   on 09_FormattedOutput.cs and the assertions in LoggingChecks.

2. Feature 8 had two names. Its id, benchmark class (08_PrepareLogger.cs)
   and chart group all said PrepareLogger, but the display name was
   "Create Logger". Since MatrixChartPaths derives the chart filename from
   the display name, the repo carried both 08-create-logger.png and a stale
   08-prepare-logger.png from before the name changed. Renamed the display
   name to "Prepare Logger" so all four agree, and dropped the orphan.

3. The overview article was two categories out of date.
   readme/art_overview/{en,ru}_overview.md claimed 6 categories, 40 libraries
   and 67 scenarios; LINQ Queries and ZIP Archives were missing from the table
   entirely and four row counts were stale. The old total was also
   self-inconsistent: its own table summed to 41, not 40. Both tables are now
   rebuilt from reports/*/features.json: 8 categories, 53 libraries, 99
   scenarios. Validation's rating leader is now Microsoft.Extensions.Validation
   rather than DataAnnotations, and the baselines paragraph gained
   System.Linq and System.IO.Compression.

README.md and the two Prepare charts are regenerated. No measurements changed:
the Name field in reports/Logging/{features,benchmarks}.json was relabelled
in place rather than re-benchmarked.

Verification

• grep -rn "Create Logger\|create-logger" returns nothing.
• dotnet build src/Matrix.Logging/Matrix.Logging.csproj succeeds with 0 warnings.
• 08-prepare-logger.png now renders with text and shows all 6 libraries
  including OpenTelemetry, with values matching the current README.
  overview-prepare.png legend reads "Prepare Logger".