docs(tally): document --regex / -r in --help text

Step 3 of plan.md (Spor B B3 pipeline run). Adds one line under
Options: in the HELP template literal so --help users can discover
the new flag. Satisfies SC #8.

[skip-docs]

plugins/ultraplan-local/examples/02-real-cli/tally.mjs

@@ -8,6 +8,7 @@ Count literal-substring occurrences of <pattern> in <file>.
 Options:
   -i, --ignore-case  Case-insensitive matching
       --lines        Count lines containing pattern (not total occurrences)
+  -r, --regex        Interpret <pattern> as a JavaScript regular expression
       --json         Emit a JSON object on stdout
   -h, --help         Show this help and exit