Regex tooling: formula gene grouping, content patches, def validation

Three regex-powered content tools (phase G5):

- Formula group functions gsum/gcount/gavg/gmin/gmax('regex') aggregate
  over every context variable whose name matches the pattern, e.g.
  gsum('leaf_.*'). Adds string literals to the formula grammar and an
  IFormulaContext.ResolveMatching hook; GenomeContext enumerates matching
  genes, so a trait can sum/average a gene group.
- DefDatabase content patches: a { "type": "Patch", patches:[{ defType,
  match (regex on defName), set:{fields} }] } file sets fields on every
  matching raw def before resolution — mods patch Core in bulk.
- DefDatabase.RegisterValidator(typeKey, field, regex): load-time check
  that a string field matches a pattern, throwing otherwise (naming/format
  conventions).

Covered by FormulaTests (group aggregation, composition, bad calls) and
DefDatabaseTests (patch set/match/unknown-type, validator pass/reject).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/MrGameEng.Core/Formulas/FormulaLexer.cs

@@ -6,6 +6,7 @@ internal enum TokenType
 {
     Number,
     Identifier,
+    String,
     Plus,
     Minus,
     Star,
@@ -99,6 +100,27 @@ internal static class FormulaLexer
                 continue;
             }
 
+            if (c == '\'')
+            {
+                var open = i;
+                var start = ++i;
+                while (i < source.Length && source[i] != '\'')
+                {
+                    i++;
+                }
+
+                if (i >= source.Length)
+                {
+                    throw new FormulaException($"Unterminated string at position {open}.");
+                }
+
+                tokens.Add(
+                    new Token(TokenType.String, open, text: source.Substring(start, i - start))
+                );
+                i++; // пропускаем закрывающую кавычку
+                continue;
+            }
+
             var pos = i;
             switch (c)
             {