Mark migration files as generated code

[glen-84]

Summary of the changes (Less than 80 chars)

• Mark migration files as generated code.

[Copilot]

Pull request overview

This PR replaces a global .editorconfig rule that suppressed all analyzer diagnostics for files under **/Migrations/**.cs with per-directory .editorconfig files in three Demo project migration directories. The new approach uses generated_code = true to mark migration files as generated code, which is the recommended Roslyn/Microsoft approach for suppressing analyzers on auto-generated files.

Changes:

• Removed the global [**/Migrations/**.cs] section from the root .editorconfig that disabled analyzer diagnostics for migration files.
• Added .editorconfig files with root = true and generated_code = true to three Demo migration directories (Billing, Catalog, Shipping).

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
.editorconfig	Removed the global migration file analyzer suppression rule
src/Mocha/src/Demo/Demo.Shipping/Migrations/.editorconfig	New nested .editorconfig marking migration files as generated code
src/Mocha/src/Demo/Demo.Catalog/Migrations/.editorconfig	New nested .editorconfig marking migration files as generated code
src/Mocha/src/Demo/Demo.Billing/Migrations/.editorconfig	New nested .editorconfig marking migration files as generated code

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 0.00%. Comparing base (6a3b7a3) to head (d617f39).
⚠️ Report is 932 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #9346       +/-   ##
==========================================
- Coverage   74.16%       0   -74.17%     
==========================================
  Files        2677       0     -2677     
  Lines      140790       0   -140790     
  Branches    16371       0    -16371     
==========================================
- Hits       104421       0   -104421     
+ Misses      30774       0    -30774     
+ Partials     5595       0     -5595     

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