[Bug]: `first=501` accepted despite schema max=500

The schema defines `entity.health.first` with `min: 1, max: 500`, and DAB correctly rejects `first=0` with `"Invalid value for first: 0. Value must be greater than 0."` However, `first=501` is accepted without error.

## Expected

DAB should reject `first=501` at config deserialization with a message like `"Invalid value for first: 501. Value must be at most 500."`

## Actual

DAB starts normally and runs health checks with `first=501`. The query becomes `SELECT TOP 502 ...`, which works but exceeds the documented maximum.

Start by reproducing configuration deserialization with entity.health.first set to 0 and 501, comparing the existing lower-bound rejection with the missing upper-bound rejection. Trace the health configuration validation path and its tests, if present. Done means first=501 is rejected with an at-most-500 message and valid values still start health checks normally.

Vom Indexierungsmodell aus dem Issue-Text verfasst.