Fix unsafe type casts via shared entityPresentationSnapshot utility

Extract entityPresentationSnapshot helper to eliminate unsafe `as Entity`
casts when passing CompoundEntityRef to EntityPresentationApi.forEntity(),
which only accepts Entity | string. The helper safely discriminates input
types and stringifies CompoundEntityRef before calling the API.

- Add entityPresentationSnapshot as a public export from catalog-react
- Remove duplicated getEntityTitle/getTitle helpers across 5 files
- Fix useAsync dependency array in TemplateFormPreviewer
- Update TSDoc across all presentation API surfaces to reference the
  new helper
- Update entity-presentation.md docs with usage guidance and migration
  table

Made-with: Cursor
Signed-off-by: Marat Dyatko <maratd@spotify.com>

plugins/techdocs/src/home/components/Tables/helpers.ts

@@ -14,13 +14,9 @@
  * limitations under the License.
  */
 
+import { RELATION_OWNED_BY, Entity } from '@backstage/catalog-model';
 import {
-  RELATION_OWNED_BY,
-  Entity,
-  stringifyEntityRef,
-} from '@backstage/catalog-model';
-import {
-  defaultEntityPresentation,
+  entityPresentationSnapshot,
   getEntityRelations,
   type EntityPresentationApi,
 } from '@backstage/plugin-catalog-react';
@@ -54,15 +50,14 @@ export function entitiesToDocsMapper(
         }),
         ownedByRelations,
         ownedByRelationsTitle: ownedByRelations
-          .map(r => {
-            if (entityPresentationApi) {
-              return entityPresentationApi.forEntity(stringifyEntityRef(r), {
-                defaultKind: 'group',
-              }).snapshot.primaryTitle;
-            }
-            return defaultEntityPresentation(r, { defaultKind: 'group' })
-              .primaryTitle;
-          })
+          .map(
+            r =>
+              entityPresentationSnapshot(
+                r,
+                { defaultKind: 'group' },
+                entityPresentationApi,
+              ).primaryTitle,
+          )
           .join(', '),
       },
     };