fix(editor): drop dead -? from srccfg number regex

The `\b` word boundary anchor prevents the optional minus from ever
matching from positions where signed numbers naturally appear (` -1`,
`(-1`, `=-1` all word-boundary-from-non-word and the `-?` fires zero
chars). Negative numbers are tokenised via the operator class instead,
which is the consistent behaviour the grammar already exhibits.
Plan source block updated to match so a fresh regeneration produces the
same file.

Addresses Minor #1 from the Task 2 code review.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

docs/superpowers/plans/2026-05-16-textarea-code-editor.md

@@ -207,7 +207,7 @@ Create `l4d2web/l4d2web/static/js/srccfg-grammar.js`:
       greedy: true,
     },
     keyword: /\b(?:exec|alias|bind|unbind|toggle)\b/,
-    number: /\b-?\d+(?:\.\d+)?\b/,
+    number: /\b\d+(?:\.\d+)?\b/,
     identifier: /\b[a-zA-Z_][a-zA-Z0-9_]*\b/,
     operator: /[+\-;]/,
   };

l4d2web/l4d2web/static/js/srccfg-grammar.js

@@ -10,7 +10,7 @@
       greedy: true,
     },
     keyword: /\b(?:exec|alias|bind|unbind|toggle)\b/,
-    number: /\b-?\d+(?:\.\d+)?\b/,
+    number: /\b\d+(?:\.\d+)?\b/,
     identifier: /\b[a-zA-Z_][a-zA-Z0-9_]*\b/,
     operator: /[+\-;]/,
   };