Suffix interfaces with Interface and traits with Trait

[Firehed]

Closes #552.

Every interface under src/ and tests/ now ends in Interface, and every trait in Trait. A PHPCS rule pins the convention so future additions cannot skip the suffix.

Layout

• First commit turns on Generic.NamingConventions.InterfaceNameSuffix and Generic.NamingConventions.TraitNameSuffix in phpcs.xml.dist.
• Each following commit does one rename: interface or trait declaration, defining file, and every consumer (source, tests, deptrac, phpstan, docs, CLAUDE.md).
• Two follow-ups fix wrapping and prose the mechanical Type pass over-reached on.

Notes

• tests/Fixtures/* is out of scope (already excluded from PHPCS) so PSR examples stay intact.
• OneRoutePerFactTest composite and layout checks now strip the Interface suffix before comparing, so SyntaxSourceInterface and its CompositeSyntaxSource still satisfy the same-family-namespace rule.
• The phpstan baseline picked up the new TypeSourceInterface deprecation text; no baseline entries were added.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.72%. Comparing base (f2bbffc) to head (54bdcd8).
⚠️ Report is 1 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff            @@
##               main     #554   +/-   ##
=========================================
  Coverage     99.72%   99.72%           
  Complexity     1909     1909           
=========================================
  Files           134      134           
  Lines          5005     5005           
=========================================
  Hits           4991     4991           
  Misses           14       14           

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[Firehed]

Overreach