A valid 30-day push gateway grant lifetime could render in scientific
notation (e.g. `2.592e+06`) in the chart, which the gateway binary does
not accept.
Always ormat the integer as decimal text, preserving the strict gateway
parser.
### Testing
Added regression coverage that feeds actual Helm-rendered environment
values into the production config parser. Covers defaults, values files,
command-line overrides, exact lifetime boundaries, and invalid input
rejection. The default case failed before the fix and passes afterward.
Signed-off-by: Tom Brow <tomb@block.xyz>
