Fix --idle-timeout-seconds validation being skipped (#8009)

The lower bound check ran before the parser had resolved the value, so it
only saw a value with the --idle-timeout-seconds=<value> form. With the
space-separated form the value was still undefined at that point,
Number(undefined) is NaN, and NaN <= 60 is false, so anything got through.

Move the check below the block that pulls the value from the next
argument so both forms are validated the same way.

CHANGELOG.md

@@ -22,6 +22,11 @@ Code v99.99.999
 
 ## Unreleased
 
+### Fixed
+
+- `--idle-timeout-seconds` was only validated when passed as `--idle-timeout-seconds=<value>`;
+  values of 60 or less passed as `--idle-timeout-seconds <value>` were silently accepted.
+
 ## [4.138.0](https://github.com/coder/code-server/releases/tag/v4.138.0) - 2026-09-19
 
 Code v1.138.0