feat(onboarding): "Project archive" PLC format + auto-detect from extension

A .projectarchive is neither PLCopen XML nor Structured Text, but the wizard's
format dropdown only offered those two — confusing when uploading a CODESYS
archive (found live during the demo).

- add PlcFormat::ProjectArchive (metadata only; processing is content-driven).
- wizard: add the "Project archive (.projectarchive)" option, and auto-select the
  format from the chosen file's extension (.projectarchive/.project → archive,
  .xml → PLCopen XML, .st/.exp/.scl → Structured Text).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

compliance-core/src/models/onboarding.rs

@@ -202,6 +202,9 @@ pub enum PlcFormat {
     PlcopenXml,
     /// IEC 61131-3 Structured Text source.
     StructuredText,
+    /// A CODESYS project archive (`.projectarchive` — a zip bundling the project
+    /// plus its referenced libraries and runtime; the source of the control-app SBOM).
+    ProjectArchive,
 }
 
 /// PLC-specific configuration for a [`ArtifactKind::PlcProject`] artifact.