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/auth.py

@@ -1,7 +1,6 @@
 # auth.py - Keep security-critical validation
 import re
 from datetime import datetime
-from typing import Optional
 
 from pydantic import BaseModel, ConfigDict, EmailStr, Field, field_validator
 
@@ -33,7 +32,7 @@ class UserRegister(BaseModel):
 class UserLogin(BaseModel):
     email_or_username: str = Field(..., description="Username or email address")
     password: str = Field(..., description="Password")
-    vendor_code: Optional[str] = Field(
+    vendor_code: str | None = Field(
         None, description="Optional vendor code for context"
     )
 
@@ -50,7 +49,7 @@ class UserResponse(BaseModel):
     username: str
     role: str
     is_active: bool
-    last_login: Optional[datetime] = None
+    last_login: datetime | None = None
     created_at: datetime
     updated_at: datetime