Unify database schema: Resolve all User model conflicts and auth table incompatibilities

Major changes:
- Consolidate 3 different User models into single unified model (models/user.py)
- Use UUID primary keys throughout (matches existing database schema)
- Add comprehensive authentication fields while preserving existing data
- Remove duplicate User model from auth.py, keep APIKey/RefreshToken/TokenBlacklist
- Update all imports to use unified User model consistently
- Create database migration (002_add_auth_fields.sql) for safe schema upgrade
- Fix frontend User interface to handle UUID string IDs
- Add backward compatibility fields (name property, role field)
- Maintain relationships for authentication features (api_keys, refresh_tokens)

Schema conflicts resolved:
✅ Migration schema (UUID, 7 fields) + Basic model (Integer, 6 fields) + Auth model (Integer, 10 fields)
   → Unified model (UUID, 12 fields with full backward compatibility)
✅ Field inconsistencies (name vs full_name) resolved with compatibility property
✅ Database foreign key constraints updated for UUID relationships
✅ JWT token handling fixed for UUID user IDs

This completes the holistic database schema unification requested after quick
patching caused conflicts. All existing data preserved, full auth system functional.

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

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

backend/migrations/002_add_auth_fields.sql

@@ -0,0 +1,103 @@
+-- Migration: Add authentication fields to existing users table
+-- This migration adds the necessary fields for the unified User model
+-- while preserving all existing data
+
+BEGIN;
+
+-- Add new columns to users table for authentication features
+ALTER TABLE users 
+ADD COLUMN IF NOT EXISTS full_name VARCHAR(255),
+ADD COLUMN IF NOT EXISTS is_superuser BOOLEAN DEFAULT FALSE,
+ADD COLUMN IF NOT EXISTS is_verified BOOLEAN DEFAULT FALSE;
+
+-- Add username column if it doesn't exist (make it nullable for existing users)
+ALTER TABLE users 
+ADD COLUMN IF NOT EXISTS username VARCHAR(50);
+
+-- Create unique index on username (partial index to handle NULLs)
+CREATE UNIQUE INDEX IF NOT EXISTS users_username_unique_idx 
+ON users (username) WHERE username IS NOT NULL;
+
+-- Update existing users to have a default username if none exists
+-- This uses email prefix as username for existing users
+UPDATE users 
+SET username = SPLIT_PART(email, '@', 1) 
+WHERE username IS NULL;
+
+-- Add role column for backward compatibility
+ALTER TABLE users 
+ADD COLUMN IF NOT EXISTS role VARCHAR(50) DEFAULT 'user';
+
+-- Create the authentication-related tables if they don't exist
+
+-- API Keys table
+CREATE TABLE IF NOT EXISTS api_keys (
+    id SERIAL PRIMARY KEY,
+    user_id UUID NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    name VARCHAR(255) NOT NULL,
+    key_hash VARCHAR(255) UNIQUE NOT NULL,
+    key_prefix VARCHAR(10) NOT NULL,
+    scopes TEXT,
+    is_active BOOLEAN DEFAULT TRUE,
+    last_used TIMESTAMP,
+    usage_count INTEGER DEFAULT 0,
+    expires_at TIMESTAMP,
+    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
+    updated_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
+);
+
+CREATE INDEX IF NOT EXISTS api_keys_user_id_idx ON api_keys(user_id);
+CREATE INDEX IF NOT EXISTS api_keys_key_hash_idx ON api_keys(key_hash);
+
+-- Refresh Tokens table
+CREATE TABLE IF NOT EXISTS refresh_tokens (
+    id SERIAL PRIMARY KEY,
+    user_id UUID NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    token_hash VARCHAR(255) UNIQUE NOT NULL,
+    jti VARCHAR(36) UNIQUE NOT NULL,
+    device_info VARCHAR(512),
+    is_active BOOLEAN DEFAULT TRUE,
+    expires_at TIMESTAMP NOT NULL,
+    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
+    last_used TIMESTAMP DEFAULT CURRENT_TIMESTAMP
+);
+
+CREATE INDEX IF NOT EXISTS refresh_tokens_user_id_idx ON refresh_tokens(user_id);
+CREATE INDEX IF NOT EXISTS refresh_tokens_token_hash_idx ON refresh_tokens(token_hash);
+CREATE INDEX IF NOT EXISTS refresh_tokens_jti_idx ON refresh_tokens(jti);
+
+-- Token Blacklist table
+CREATE TABLE IF NOT EXISTS token_blacklist (
+    id SERIAL PRIMARY KEY,
+    jti VARCHAR(36) UNIQUE NOT NULL,
+    token_type VARCHAR(20) NOT NULL,
+    expires_at TIMESTAMP NOT NULL,
+    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
+);
+
+CREATE INDEX IF NOT EXISTS token_blacklist_jti_idx ON token_blacklist(jti);
+CREATE INDEX IF NOT EXISTS token_blacklist_expires_at_idx ON token_blacklist(expires_at);
+
+-- Create function to automatically update updated_at timestamp
+CREATE OR REPLACE FUNCTION update_updated_at_column()
+RETURNS TRIGGER AS $$
+BEGIN
+    NEW.updated_at = CURRENT_TIMESTAMP;
+    RETURN NEW;
+END;
+$$ language 'plpgsql';
+
+-- Create triggers for updated_at columns
+DROP TRIGGER IF EXISTS update_users_updated_at ON users;
+CREATE TRIGGER update_users_updated_at 
+    BEFORE UPDATE ON users 
+    FOR EACH ROW 
+    EXECUTE FUNCTION update_updated_at_column();
+
+DROP TRIGGER IF EXISTS update_api_keys_updated_at ON api_keys;
+CREATE TRIGGER update_api_keys_updated_at 
+    BEFORE UPDATE ON api_keys 
+    FOR EACH ROW 
+    EXECUTE FUNCTION update_updated_at_column();
+
+COMMIT;