fix: update entity naming conventions to use singular form for consistency

kb/CONVENTIONS.md

@@ -60,7 +60,7 @@ There is no `## Siehe auch` region any more. It was the reciprocal half of a bid
 ## Naming
 
 - Human-readable titles with spaces: `Hybrid Search.md`, `Gitea Actions.md` - not kebab-case.
-- Singular for entities: `ha-core.md`, not `ha-cores.md`.
+- Singular for entities: `HA Integration.md`, not `HA Integrations.md`.
 - Comparison pages read as a comparison: `Go vs Rust.md`.
 - A decision (`concept_type: decision`) is named like any other concept - no `adr-NNN-` prefix.
   See [kb/concepts/COLLECTION.md § Decisions](concepts/COLLECTION.md#decisions).

kb/entities/COLLECTION.md

@@ -80,4 +80,4 @@ the *why* lives, and the entity page should not restate it.
 - A pattern, protocol, architecture or decision - those are concepts, even when only one entity
   uses them.
 - A page about a source document - that is a `source` page in `kb/sources/`.
-- Singular naming is required: `ha-core.md`, not `ha-cores.md`.
+- Singular naming is required: `HA Integration.md`, not `HA Integrations.md`.