docs: #91: add report about bug with rounding of the tracked hours

time-tracker/reports/bug-with-rounding-of-the-tracked-hours.md

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+# Report: Time Tracking Calculation Error For Invoices
+
+## Context
+After the implementation of the new logic for calculating tracked task hours, there were discrepancies in the invoices service for April. For example, the tracked time of employee Yulia changed from 7.16 hours (confirmed by manual calculation) to 7 hours in the system.
+
+## Cause of error
+
+GetDurationInMinutes() returned an int for TrackedMinutes.
+
+```c#
+public int GetDurationInMinutes()
+{
+    return (int)(EndTime - StartTime).TotalMinutes;
+}
+```
+
+```c#
+TrackedHours = TrackedMinutes / 60  // int / int = int (decimal part discarded)
+```
+
+When converting minutes to hours, both operands were integers, causing C# to perform integer division.
+
+For example: 430 minutes = 7.16 hours → integer division gave 7 hours (lost 0.16 hours)
+
+## Decision
+Changed the data type from int to decimal throughout the calculation chain to preserve fractional minutes.
+
+```c#
+// Changed int to decimal
+public decimal GetDurationInMinutes()
+{
+    return (decimal)(EndTime - StartTime).TotalMinutes;
+}
+```
+
+```c#
+TrackedHours = TrackedMinutes / 60  // decimal / int = decimal (decimal part not discarded)
+```
+
+After that, the tracked hours will not be rounded to an integer number.