Add job application quick reference for storing profile links and experience

Auth-protected CRUD for personal info (LinkedIn, GitHub, etc.) and
experience entries, stored in the database so nothing sensitive is in
the public repo. Displayed as a categorized panel on the Job Applications page.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/graph/schema/job_app_reference.graphql

@@ -0,0 +1,23 @@
+type JobAppReference {
+  id: ID!
+  createdAt: Time!
+  updatedAt: Time!
+  category: String!
+  label: String!
+  value: String!
+  sortOrder: Int!
+}
+
+input CreateJobAppReferenceInput {
+  category: String!
+  label: String!
+  value: String!
+  sortOrder: Int
+}
+
+input UpdateJobAppReferenceInput {
+  category: String
+  label: String
+  value: String
+  sortOrder: Int
+}