feat(products): improve replenishment-aware shopping suggestions

Replace product weight and repurchase intent fields with per-package remaining levels and inventory-first restock signals. Enrich shopping suggestions with usage-aware replenishment scoring so the frontend and LLM can prioritize real gaps and near-empty staples more reliably.

backend/alembic/versions/9f3a2c1b4d5e_replace_product_weights_with_inventory_remaining_level.py

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+"""replace product weights with inventory remaining level
+
+Revision ID: 9f3a2c1b4d5e
+Revises: 7e6f73d1cc95
+Create Date: 2026-03-08 12:00:00.000000
+
+"""
+
+from typing import Sequence, Union
+
+import sqlalchemy as sa
+
+from alembic import op
+
+# revision identifiers, used by Alembic.
+revision: str = "9f3a2c1b4d5e"
+down_revision: Union[str, Sequence[str], None] = "7e6f73d1cc95"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    bind = op.get_bind()
+    remaining_level_enum = sa.Enum(
+        "HIGH",
+        "MEDIUM",
+        "LOW",
+        "NEARLY_EMPTY",
+        name="remaininglevel",
+    )
+    remaining_level_enum.create(bind, checkfirst=True)
+
+    op.add_column(
+        "product_inventory",
+        sa.Column("remaining_level", remaining_level_enum, nullable=True),
+    )
+    op.drop_column("product_inventory", "last_weighed_at")
+    op.drop_column("product_inventory", "current_weight_g")
+    op.drop_column("products", "personal_repurchase_intent")
+    op.drop_column("products", "empty_weight_g")
+    op.drop_column("products", "full_weight_g")
+
+
+def downgrade() -> None:
+    bind = op.get_bind()
+    remaining_level_enum = sa.Enum(
+        "HIGH",
+        "MEDIUM",
+        "LOW",
+        "NEARLY_EMPTY",
+        name="remaininglevel",
+    )
+
+    op.add_column(
+        "products",
+        sa.Column("personal_repurchase_intent", sa.Boolean(), nullable=True),
+    )
+    op.add_column(
+        "product_inventory",
+        sa.Column("current_weight_g", sa.Float(), nullable=True),
+    )
+    op.add_column(
+        "product_inventory",
+        sa.Column("last_weighed_at", sa.Date(), nullable=True),
+    )
+    op.add_column("products", sa.Column("full_weight_g", sa.Float(), nullable=True))
+    op.add_column("products", sa.Column("empty_weight_g", sa.Float(), nullable=True))
+    op.drop_column("product_inventory", "remaining_level")
+    remaining_level_enum.drop(bind, checkfirst=True)