feat: improve CI and project automation workflows (#390)

- Harden docker/release workflow with manual release guardrails and concurrency
- Add stale issue cleanup workflow (issues only)
- Add project field sync workflow from issue labels
- Add weekly triage report workflow
- Add CODEOWNERS for automatic review routing

.github/CODEOWNERS

@@ -0,0 +1,11 @@
+# MedAssist ownership
+# This routes review requests automatically to the maintainer.
+
+* @DanielVolz
+
+# Explicit domains for clarity
+/backend/ @DanielVolz
+/frontend/ @DanielVolz
+/.github/ @DanielVolz
+/doku/ @DanielVolz
+/docs/ @DanielVolz