FireWatch: Grass Fuel Types

**Actual Behaviour**

Users have been creating FireWatch's with O1A/B, leading to errors in the FBP calculations because the reference station may not have grass curing set

**Steps To Reproduce**

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**Screenshots**

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**Expected Behaviour**

A clear and concise description of what you expected to happen.

The issue names no files, tests, or entry points. Start by obtaining concrete reproduction steps for FireWatch using O1A/B, then trace the FBP calculation path when the reference station lacks grass curing. Done means the reported calculation error is prevented and the behavior is covered by a regression test.

Written by the indexing model from the issue text.