fix: rename contributing/license pages to avoid Mintlify reserved slug conflict

mint export fails with 'file does not exist' for pages named 'contributing'
and 'license' — these are reserved by Mintlify's GitHub integration layer.
Renamed to contributing-guide.md and project-license.md and updated all
nav entries and cross-links throughout the docs.

Also adds .gitattributes LF rules to prevent CRLF issues from Windows devs.

docs/docs.json

@@ -194,10 +194,10 @@
             "pages": [
               "community",
               "community-projects",
-              "contributing",
+              "contributing-guide",
               "governance",
               "citation",
-              "license"
+              "project-license"
             ]
           }
         ]