refactor: modernize code quality tooling with Ruff

- Replace black, isort, and flake8 with Ruff (all-in-one linter and formatter)
- Add comprehensive pyproject.toml configuration
- Simplify Makefile code quality targets
- Configure exclusions for venv/.venv in pyproject.toml
- Auto-fix 1,359 linting issues across codebase

Benefits:
- Much faster builds (Ruff is written in Rust)
- Single tool replaces multiple tools
- More comprehensive rule set (UP, B, C4, SIM, PIE, RET, Q)
- All configuration centralized in pyproject.toml
- Better import sorting and formatting consistency

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

models/schema/inventory.py

@@ -1,6 +1,5 @@
 # models/schema/inventory.py
 from datetime import datetime
-from typing import List, Optional
 
 from pydantic import BaseModel, ConfigDict, Field
 
@@ -27,9 +26,9 @@ class InventoryAdjust(InventoryBase):
 class InventoryUpdate(BaseModel):
     """Update inventory fields."""
 
-    quantity: Optional[int] = Field(None, ge=0)
-    reserved_quantity: Optional[int] = Field(None, ge=0)
-    location: Optional[str] = None
+    quantity: int | None = Field(None, ge=0)
+    reserved_quantity: int | None = Field(None, ge=0)
+    location: str | None = None
 
 
 class InventoryReserve(BaseModel):
@@ -49,7 +48,7 @@ class InventoryResponse(BaseModel):
     location: str
     quantity: int
     reserved_quantity: int
-    gtin: Optional[str]
+    gtin: str | None
     created_at: datetime
     updated_at: datetime
 
@@ -70,16 +69,16 @@ class ProductInventorySummary(BaseModel):
 
     product_id: int
     vendor_id: int
-    product_sku: Optional[str]
+    product_sku: str | None
     product_title: str
     total_quantity: int
     total_reserved: int
     total_available: int
-    locations: List[InventoryLocationResponse]
+    locations: list[InventoryLocationResponse]
 
 
 class InventoryListResponse(BaseModel):
-    inventories: List[InventoryResponse]
+    inventories: list[InventoryResponse]
     total: int
     skip: int
     limit: int