Leading Marked as Mass Noun when it is an Adjective

**What got flagged?**
```
Each leading 1 ...
^^^^^^^^^^^^ `leading` is a mass noun. (Harper MassNouns)
```

**Why is this incorrect?**
Leading is being used as an adjective, not as a mass noun.

**Example of correct usage:**
Each leading 1 comes in a column to the right of the leading 1s in rows above it.

Start by reproducing the example with the Harper MassNouns rule and locate where that rule classifies “leading.” Confirm the adjective use is accepted while valid mass-noun uses remain flagged; add or update the relevant regression test if the repository provides one.

Written by the indexing model from the issue text.