feat: add template_of getter + bump to v0.3.0

Add composition.template_of(entity) -> string|nil, returning the
template-id this entity was created from. Returns nil for
non-composition-managed entities (e.g. raw entity.create() handles)
and loud-errors on nil arg. Enables crafting and inventory consumers
to recover the template-id without round-tripping through tags.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

manifest.lib

@@ -1 +1 @@
-{"id":"lib-core.composition","version":"0.2.0","api_min":"0.1","deps":[]}
+{"id":"lib-core.composition","version":"0.3.0","api_min":"0.1","deps":[]}