Add package-map for cross-repo SCIP navigation

- Add package-map.edn mapping namespaces to their packages
- Update CI workflow to pass package-map when generating SCIP index
- Enables cross-repo navigation to clojure-tui in Sourcegraph

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

package-map.edn

@@ -0,0 +1,9 @@
+;; Package map for cross-repository SCIP navigation
+;; Maps namespace prefixes to package@version coordinates
+;;
+;; This enables Sourcegraph to resolve cross-repo references:
+;; - "tui" prefix -> clojure-tui repository
+;; - "lazygitclj" prefix -> this repository
+
+{"tui" "io.github.ajet/clojure-tui@main"
+ "lazygitclj" "io.github.ajet/lazygitclj@main"}