chore: import upstream snapshot with attribution

CITATION.cff

@@ -0,0 +1,31 @@
+cff-version: 1.2.0
+message: >-
+  If you use Spec Kit in your research or reference it in a paper,
+  please cite it using the metadata below.
+type: software
+title: "Spec Kit"
+abstract: >-
+  Spec Kit is an open source toolkit for Spec-Driven Development (SDD) —
+  a methodology that helps software teams build high-quality software faster
+  by focusing on product scenarios and predictable outcomes. It provides the
+  Specify CLI, slash-command templates, extensions, presets, workflows, and
+  integrations for popular AI coding agents.
+authors:
+  - given-names: Den
+    family-names: Delimarsky
+    alias: localden
+  - given-names: Manfred
+    family-names: Riem
+    alias: mnriem
+repository-code: "https://github.com/github/spec-kit"
+url: "https://github.github.io/spec-kit/"
+license: MIT
+version: "0.10.2"
+date-released: "2026-06-11"
+keywords:
+  - spec-driven development
+  - ai coding agents
+  - software engineering
+  - cli
+  - copilot
+  - specification