ci: rename .github/workflows -> .gitea/workflows (post-suspension sweep)

GitHub org Molecule-AI was suspended 2026-05-06; SCM moved to Gitea
(git.moleculesai.app). The wholesale `git push --mirror` migration left
workflow files under .github/workflows/, which Gitea Actions does NOT
read - it reads .gitea/workflows/ exclusively.

This rename + the cross-repo `uses:` path rewrite are the minimum
edits to make CI fire on this repo again. The workflow content itself
is not modified (other than the path rewrites and lowercasing of the
old `Molecule-AI` org reference to the post-suspension `molecule-ai`).

Refs: feedback_post_suspension_migration_must_sweep_dormant_repos

.gitea/workflows/secret-scan.yml

@@ -19,4 +19,4 @@ on:
 
 jobs:
   secret-scan:
-    uses: Molecule-AI/molecule-core/.github/workflows/secret-scan.yml@staging
+    uses: molecule-ai/molecule-core/.gitea/workflows/secret-scan.yml@staging