feat(mappings): strict validation + silent CSV skip for missing CODMAT

Add Pydantic validators and service-level checks that reject empty SKU/CODMAT
on create/edit (400). CSV import now silently skips rows without CODMAT and
counts them in skipped_no_codmat instead of treating them as errors.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

api/app/routers/mappings.py

@@ -2,7 +2,7 @@ from fastapi import APIRouter, Query, Request, UploadFile, File
 from fastapi.responses import StreamingResponse, HTMLResponse, JSONResponse
 from fastapi.templating import Jinja2Templates
 from fastapi import HTTPException
-from pydantic import BaseModel
+from pydantic import BaseModel, validator
 from pathlib import Path
 from typing import Optional
 import io
@@ -21,6 +21,12 @@ class MappingCreate(BaseModel):
     cantitate_roa: float = 1
     procent_pret: float = 100
 
+    @validator('sku', 'codmat')
+    def not_empty(cls, v):
+        if not v or not v.strip():
+            raise ValueError('nu poate fi gol')
+        return v.strip()
+
 class MappingUpdate(BaseModel):
     cantitate_roa: Optional[float] = None
     procent_pret: Optional[float] = None
@@ -32,6 +38,12 @@ class MappingEdit(BaseModel):
     cantitate_roa: float = 1
     procent_pret: float = 100
 
+    @validator('new_sku', 'new_codmat')
+    def not_empty(cls, v):
+        if not v or not v.strip():
+            raise ValueError('nu poate fi gol')
+        return v.strip()
+
 class MappingLine(BaseModel):
     codmat: str
     cantitate_roa: float = 1