sync(launcher-test): markdown.lua picks up image_missing localization

markdown.lua now mirrors the launcher byte-for-byte: M.render takes an
optional t 6th arg that the launcher threads its ctx.t through for the
image-missing placeholder. Pure-additive parameter — existing test
callers (which never invoke M.render) are unaffected.

manifest.lib: bump 0.2.0 -> 0.3.0. The render-signature change is
API-shaped; downstream consumers that call the helper directly may want
to opt in to the new arg.

manifest.lib

@@ -1,7 +1,7 @@
 {
     "id": "lib-management.launcher-test",
     "role": "test",
-    "version": "0.2.0",
+    "version": "0.3.0",
     "api_min": "0.1",
     "deps": []
 }