feat: .kc Layer 1 — manifest auto-creation and platform file associations

kc_format.py:
- Auto-create silo/manifest.json with default fields (UUID, timestamps,
  username) when saving a .kc file that lacks one
- Update modified_at timestamp on each save
- KC_VERSION = 1.0

Platform integration:
- kindred-create.desktop: add application/x-kindred-create MIME type
- kindred-create.xml: register .kc glob patterns with dedicated MIME type
  (application/x-kindred-create), separate from .fcstd type

resources/kindred-create.desktop

@@ -7,7 +7,7 @@ Icon=kindred-create
 Terminal=false
 Type=Application
 Categories=Graphics;Science;Engineering;
-MimeType=application/x-extension-fcstd;x-scheme-handler/kindred;
+MimeType=application/x-extension-fcstd;application/x-kindred-create;x-scheme-handler/kindred;
 Keywords=CAD;3D;modeling;engineering;design;parametric;
 StartupNotify=true
 StartupWMClass=KindredCreate

resources/kindred-create.xml

@@ -1,11 +1,18 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <mime-info xmlns="http://www.freedesktop.org/standards/shared-mime-info">
   <mime-type type="application/x-extension-fcstd">
-    <comment>Kindred Create Document</comment>
-    <comment xml:lang="en">Kindred Create Document</comment>
+    <comment>FreeCAD Document</comment>
+    <comment xml:lang="en">FreeCAD Document</comment>
     <icon name="kindred-create"/>
     <glob pattern="*.FCStd"/>
     <glob pattern="*.fcstd"/>
     <glob pattern="*.FCSTD"/>
   </mime-type>
+  <mime-type type="application/x-kindred-create">
+    <comment>Kindred Create Document</comment>
+    <comment xml:lang="en">Kindred Create Document</comment>
+    <icon name="kindred-create"/>
+    <glob pattern="*.kc"/>
+    <glob pattern="*.KC"/>
+  </mime-type>
 </mime-info>