Add bilingual manual and localized docs routes

doc/manual/source/language/value/string.md

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+# String
+
+`String` is the primitive type constraint for string values.
+
+A string literal is enclosed in `"`.
+
+```dcdl
+"hello"
+"line 1\nline 2"
+```
+
+`$`, `{`, and `}` have no special meaning inside a string; Decodal does not perform string interpolation.
+
+## Examples
+
+```dcdl
+name = String;
+greeting = String default "hello";
+```
+
+## Constraint composition
+
+`String` can be composed with string constraints.
+
+```dcdl
+message = String & /Hello! .*/;
+```
+
+Enable regex-constraint validation with the Rust crate's `regex` feature.
+Without that feature, a regex constraint cannot be validated against a concrete string and produces a diagnostic.