Fix the import I omitted in the locale-reachable portability fix

My previous commit changed the REPO fallback to
resolve(dirname(fileURLToPath(import.meta.url)), '..') but did not add the
fileURLToPath import, so the gate died at load with

    ReferenceError: fileURLToPath is not defined

and I pushed it. node --check passed because that is a RUNTIME error, not a
syntax one, and check:no-abs-paths went green because the offending literal
really was gone -- so both of the checks I ran said yes while the gate
itself could no longer run at all. The script's own exit code printed 1 in
the same output I pushed from, and I did not stop on it.

Verified this time by running the gate, not around it:
check:locale-reachable 0, check:no-abs-paths 0.

internal/check-locale-reachable.mjs

@@ -16,6 +16,7 @@
 //      lang-less, the URL path alone would silently become the only way in.
 import { readFileSync, readdirSync, existsSync } from 'node:fs'
 import { resolve, join, dirname } from 'node:path'
+import { fileURLToPath } from 'node:url'
 
 const REPO = process.env.DOXA_REPO
   // FOURTH instance of this pattern in one flight (check-zone-census, check-share-policy,