Add backend validation for note length using constant

- Updated BookingRequest validator to use NOTE_MAX_LENGTH constant
- Replaced hardcoded 144 with constant for consistency
- Error message now includes the actual max length value

backend/schemas.py

@@ -4,6 +4,8 @@ from typing import Generic, TypeVar
 
 from pydantic import BaseModel, EmailStr, field_validator
 
+from shared_constants import NOTE_MAX_LENGTH
+
 
 class UserCredentials(BaseModel):
     """Base model for user email/password."""
@@ -207,8 +209,8 @@ class BookingRequest(BaseModel):
     @field_validator("note")
     @classmethod
     def validate_note_length(cls, v: str | None) -> str | None:
-        if v is not None and len(v) > 144:
-            raise ValueError("Note must be at most 144 characters")
+        if v is not None and len(v) > NOTE_MAX_LENGTH:
+            raise ValueError(f"Note must be at most {NOTE_MAX_LENGTH} characters")
         return v