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>

README.md

@@ -5,7 +5,7 @@ property defaults; `create` spawns an `engine.entity` with template
 defaults + per-instance overrides; entities are indexed by template-id
 and tag for cheap reverse-lookup.
 
-**Version:** 0.2.0
+**Version:** 0.3.0
 **Lib-ID:** lib-core.composition
 **Requires:** (none — uses engine `entity.*`, `domain.contribute` only)
 **Tags:** composition, entity, template, tag-index
@@ -21,15 +21,16 @@ graph LR
 ```
 <!-- topology:end -->
 
-## Scope (v0.2.0)
+## Scope (v0.3.0)
 
-Template-Only-Subset + set_tag + container declaration.
+Template-Only-Subset + set_tag + container declaration + template-id reverse-lookup.
 
 **Supported:**
 - `define_template{id, properties, tags}`
 - `define_template{..., container={kind="list"}}` — v0.2: `kind="list"` accepted
 - `create{template, properties}`
 - `list_by_template(id)`, `list_by_tag(tag)`
+- `template_of(entity)` — v0.3: read back the template-id an entity was created from
 - `destroy(entity)`
 - `set_tag(entity, tag, present)` — v0.2: runtime tag add/remove
 - `get_container(entity)` — v0.2: read back the container block from entity's template
@@ -151,6 +152,28 @@ end
 declared `tag` in its `tags` array. Used by `lib-core.render`
 `draw_entities{tag="..."}` (see A.2). Empty list if tag has no entities.
 
+### `composition.template_of(entity)`
+
+**Syntax:** `composition.template_of(entity) -> string or nil`
+
+**Example:**
+```lua
+local sign = composition.create{ template = "sign" }
+local tpl_id = composition.template_of(sign)
+-- tpl_id == "sign"
+
+local raw = entity.create()
+local none = composition.template_of(raw)
+-- none == nil  (raw entities are not composition-managed)
+```
+
+**Description:** Returns the template-id this entity was created from,
+or `nil` if the entity is not composition-managed (e.g. a raw
+`entity.create()` handle, or an entity whose composition meta-record
+has already been cleared via `destroy`). Loud-Error if `entity` is `nil`.
+Used by crafting / inventory / recipe code that needs to recover the
+template-id without round-tripping through tags.
+
 ### `composition.set_tag(entity, tag, present)`
 
 **Syntax:** `composition.set_tag(entity, tag: string, present: boolean) -> void`