feat(backend): champs identified_* sur Media pour stocker l'identification

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

backend/app/models/media.py

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+from datetime import datetime, timezone
+from typing import Optional
+from sqlmodel import Field, SQLModel
+
+
+class Media(SQLModel, table=True):
+    id: Optional[int] = Field(default=None, primary_key=True)
+    entity_type: str  # jardin|plante|outil|plantation
+    entity_id: int
+    url: str
+    thumbnail_url: Optional[str] = None
+    titre: Optional[str] = None
+    # Identification automatique
+    identified_species: Optional[str] = None
+    identified_common: Optional[str] = None
+    identified_confidence: Optional[float] = None
+    identified_source: Optional[str] = None  # "plantnet" | "yolo" | "cache"
+    created_at: datetime = Field(default_factory=lambda: datetime.now(timezone.utc))
+
+
+class Attachment(SQLModel, table=True):
+    id: Optional[int] = Field(default=None, primary_key=True)
+    entity_type: str
+    entity_id: int
+    type: str  # pdf|url|note
+    titre: Optional[str] = None
+    contenu: Optional[str] = None
+    created_at: datetime = Field(default_factory=lambda: datetime.now(timezone.utc))