refactor(annotations): remove overlap check to allow intersecting regions

Historical letter lines often intersect, so the system must support
overlapping annotation regions. Removed the overlap guard from
createAnnotation(), deleted ErrorCode.ANNOTATION_OVERLAP, and cleaned
up all tests and frontend error mappings that referenced it.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/messages/de.json

@@ -1,7 +1,6 @@
 {
 	"$schema": "https://inlang.com/schema/inlang-message-format",
 	"error_annotation_not_found": "Die Annotation wurde nicht gefunden.",
-	"error_annotation_overlap": "Die Annotation überschneidet sich mit einer vorhandenen.",
 	"annotation_outdated_notice": "Einige Annotationen beziehen sich auf eine frühere Dateiversion und werden nicht angezeigt.",
 	"error_document_not_found": "Das Dokument wurde nicht gefunden.",
 	"error_document_no_file": "Diesem Dokument ist noch keine Datei zugeordnet.",

frontend/messages/en.json

@@ -1,7 +1,6 @@
 {
 	"$schema": "https://inlang.com/schema/inlang-message-format",
 	"error_annotation_not_found": "Annotation not found.",
-	"error_annotation_overlap": "The annotation overlaps an existing one.",
 	"annotation_outdated_notice": "Some annotations refer to an earlier file version and are not shown.",
 	"error_document_not_found": "Document not found.",
 	"error_document_no_file": "No file is associated with this document.",

frontend/messages/es.json

@@ -1,7 +1,6 @@
 {
 	"$schema": "https://inlang.com/schema/inlang-message-format",
 	"error_annotation_not_found": "Anotación no encontrada.",
-	"error_annotation_overlap": "La anotación se superpone con una existente.",
 	"annotation_outdated_notice": "Algunas anotaciones hacen referencia a una versión anterior del archivo y no se muestran.",
 	"error_document_not_found": "Documento no encontrado.",
 	"error_document_no_file": "No hay ningún archivo asociado a este documento.",

frontend/src/lib/errors.ts

@@ -18,7 +18,6 @@ export type ErrorCode =
 	| 'IMPORT_ALREADY_RUNNING'
 	| 'INVALID_RESET_TOKEN'
 	| 'ANNOTATION_NOT_FOUND'
-	| 'ANNOTATION_OVERLAP'
 	| 'TRANSCRIPTION_BLOCK_NOT_FOUND'
 	| 'TRANSCRIPTION_BLOCK_CONFLICT'
 	| 'COMMENT_NOT_FOUND'
@@ -82,8 +81,6 @@ export function getErrorMessage(code: ErrorCode | string | undefined): string {
 			return m.error_invalid_reset_token();
 		case 'ANNOTATION_NOT_FOUND':
 			return m.error_annotation_not_found();
-		case 'ANNOTATION_OVERLAP':
-			return m.error_annotation_overlap();
 		case 'TRANSCRIPTION_BLOCK_NOT_FOUND':
 			return m.error_transcription_block_not_found();
 		case 'TRANSCRIPTION_BLOCK_CONFLICT':