fix(workflows): gate prompt uses isdecimal() so a superscript digit doesn't crash (#3624)

The interactive gate prompt guarded numeric choices with raw.isdigit(), but
str.isdigit() returns True for characters int() rejects — superscripts/subscripts
like '²'. So typing '²' passed the guard and int('²') raised an uncaught
ValueError, crashing the prompt loop. Use raw.isdecimal(), which is exactly the
decimal-digit set int() accepts (Numeric_Type=Decimal), so such input is treated
as an invalid choice and re-prompted. No behavior change for valid input.

Test: input '²' then '1' returns the first option (fails before: ValueError).

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/specify_cli/workflows/steps/gate/__init__.py

@@ -168,7 +168,11 @@ class GateStep(StepBase):
             except (EOFError, KeyboardInterrupt):
                 print()
                 return options[-1]  # default to last (usually reject)
-            if raw.isdigit() and 1 <= int(raw) <= len(options):
+            # isdecimal() (not isdigit()): int() accepts exactly the decimal-digit
+            # set, whereas isdigit() also returns True for superscripts/subscripts
+            # (e.g. "²") that int() then rejects with ValueError — crashing
+            # this interactive loop.
+            if raw.isdecimal() and 1 <= int(raw) <= len(options):
                 return options[int(raw) - 1]
             # Also accept the option name directly
             if raw.lower() in [o.lower() for o in options]: