feat: add generic Value[T] base class for value objects

- Create Value[T] (frozen dataclass + ABC + Generic) in domain/framework/
- Migrate ClassifiedAdTitle and ClassifiedAdText to inherit Value[str]
- Standardize all value access via .value instead of type-specific fields

domain/marketplace/classified_ad_title.py

@@ -1,10 +1,12 @@
 from dataclasses import dataclass
 
+from domain.framework.value import Value
+
 
 @dataclass(frozen=True)
-class ClassifiedAdTitle:
-    title: str
-
+class ClassifiedAdTitle(Value[str]):
     def __post_init__(self):
-        if len(self.title) > 100:
-            raise ValueError(f"Title cannot be longer than 100 characters: {self.title}")
+        if len(self.value) > 100:
+            raise ValueError(
+                f"Title cannot be longer than 100 characters: {self.value}"
+            )