feat: release notes

Each release can carry notes in Markdown, written before or after it
ships. A draft is generated from its finished tickets grouped by type, to
edit and copy from the releases page.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

libs/api/tracker/presenters/src/lib/http/dto/requests.dto.ts

@@ -857,6 +857,19 @@ export class CreateReleaseDto {
 
 export class UpdateReleaseDto extends PartialType(CreateReleaseDto) {}
 
+export class ReleaseNotesDto {
+  @ApiProperty({
+    type: String,
+    nullable: true,
+    maxLength: 20000,
+    description: 'Markdown; null removes the notes',
+  })
+  @ValidateIf((dto: ReleaseNotesDto) => dto.notes !== null)
+  @IsString()
+  @MaxLength(20000)
+  notes!: string | null;
+}
+
 const DAY = /^\d{4}-\d{2}-\d{2}$/;
 
 export class CreateSprintDto {