[AZ-372] Add .editorconfig, Directory.Build.props, format/coverage wiring

Wires the C19 tooling baseline so dotnet format and Coverlet gate the
test script and a small NetAnalyzers ruleset (CA1001, CA1051, CA1816,
CA2227) at warning severity is visible from the next build.

- .editorconfig (new, root=true): whitespace rules, per-extension
  indent sizes, C# style preferences as suggestions, initial CA rules.
- Directory.Build.props (new): EnableNETAnalyzers=true,
  AnalysisLevel=latest, AnalysisMode=None so only rules explicitly
  enabled in .editorconfig fire; EnforceCodeStyleInBuild=false to keep
  build clean from style.
- scripts/run-tests.sh: Step 0 runs dotnet format whitespace
  --verify-no-changes via Docker SDK; unit/integration test calls now
  collect XPlat Code Coverage into TestResults/. New --skip-format
  escape hatch.
- .gitignore: TestResults/, coverage.cobertura.xml, *.coverage.
- SatelliteProvider.Tests/ToolingConfigurationTests.cs (new, 6 tests):
  runtime assertions that the config files, script wiring, and
  coverlet.collector reference are all in place; mirrors the
  AcceptanceCriteriaRT2Tests pattern.

Whitespace cleanup that the new format gate uncovers is staged for the
next commit (per AZ-372 spec: "commit cleanup as a separate batch").

Co-authored-by: Cursor <cursoragent@cursor.com>

Directory.Build.props

@@ -0,0 +1,10 @@
+<Project>
+
+  <PropertyGroup>
+    <EnableNETAnalyzers>true</EnableNETAnalyzers>
+    <AnalysisLevel>latest</AnalysisLevel>
+    <AnalysisMode>None</AnalysisMode>
+    <EnforceCodeStyleInBuild>false</EnforceCodeStyleInBuild>
+  </PropertyGroup>
+
+</Project>