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>

init.lua

@@ -1,5 +1,5 @@
 -- =====================================================================
--- lib-core.composition v0.2.0 — Template + Instantiation + Tag-Index
+-- lib-core.composition v0.3.0 — Template + Instantiation + Tag-Index
 -- See: meta/docs/superpowers/specs/2026-06-09-phase-A-inactive-entities-...
 --
 -- v0.1.0 Template-Only-Subset:
@@ -23,6 +23,11 @@
 --     All constraint fields (weight_max, volume_max, grid, accepts_fluid,
 --     accepts_gas, restrictions) → Loud-Error (Phase F/G deferred).
 --
+-- v0.3.0 additions:
+--   - composition.template_of(entity) — returns the template_id this
+--     entity was created from, or nil if the entity is not
+--     composition-managed. Loud-Error if entity is nil.
+--
 -- DEFERRED (loud-error if attempted):
 --   - slots         → Phase D Trigger (Composite Items with Sub-Items)
 --   - container constraint fields (weight_max, volume_max, grid,
@@ -353,6 +358,24 @@ function M.list_by_tag(tag)
     return out
 end
 
+-- Returns the template_id this entity was created from, or nil if
+-- the entity is not composition-managed (no reg_id property).
+-- Loud-Error if entity is nil.
+function M.template_of(target_entity)
+    if target_entity == nil then
+        error("composition.template_of: entity must not be nil", 2)
+    end
+    local reg_id = target_entity:get_property("composition.reg_id")
+    if not reg_id or reg_id == 0 then
+        return nil
+    end
+    local meta = entity_meta[reg_id]
+    if not meta then
+        return nil
+    end
+    return meta.template_id
+end
+
 -- Remove entity from indices + destroy engine-side. Idempotent.
 local function remove_from_list(list, entity)
     if not list then return end