ci: add workflow_dispatch trigger to release.yml

lets the auto-release job dispatch release.yml manually via gh cli.
without this, the 'Trigger release workflow' step in ci.yml fails
with HTTP 422 (Workflow does not have 'workflow_dispatch' trigger).
the tag push still triggers release.yml on its own, so this is purely
to make the auto-release step succeed cleanly.

Author: kaizen403

.github/workflows/release.yml

@@ -4,6 +4,11 @@ on:
   push:
     tags:
       - 'v*'
+  workflow_dispatch:
+    inputs:
+      tag:
+        description: 'Tag to release (e.g. v0.1.52)'
+        required: true
 
 permissions:
   contents: write