feat: add database table prefix and complete schema definition

Added `tool_ocr_` prefix to all database tables for clear separation
from other systems in the same database.

Changes:
- All tables now use `tool_ocr_` prefix
- Added tool_ocr_sessions table for token management
- Created complete SQL schema file with:
  - Full table definitions with comments
  - Indexes for performance
  - Views for common queries
  - Stored procedures for maintenance
  - Audit log table (optional)

New files:
- database_schema.sql: Ready-to-use SQL script for deployment

Configuration:
- Added DATABASE_TABLE_PREFIX environment variable
- Updated all references to use prefixed table names

Benefits:
- Clear namespace separation in shared databases
- Easier identification of Tool_OCR tables
- Prevent conflicts with other applications

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

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

openspec/changes/migrate-to-external-api-authentication/tasks.md

@@ -5,21 +5,23 @@
   - Export current schema and data
   - Document any important data to preserve
 - [ ] 1.2 Drop old tables
-  - Remove existing users table
-  - Remove any related tables
+  - Remove existing tables with old naming convention
   - Clear database for fresh start
-- [ ] 1.3 Create new database schema
-  - Create new `users` table (email as primary identifier)
-  - Create `ocr_tasks` table with user association
-  - Create `task_files` table for file tracking
+- [ ] 1.3 Create new database schema with `tool_ocr_` prefix
+  - Create new `tool_ocr_users` table (email as primary identifier)
+  - Create `tool_ocr_tasks` table with user association
+  - Create `tool_ocr_task_files` table for file tracking
+  - Create `tool_ocr_sessions` table for token storage
   - Add proper indexes for performance
 - [ ] 1.4 Create SQLAlchemy models
-  - User model (simplified)
-  - Task model with user relationship
-  - TaskFile model with cascade delete
+  - User model (mapped to `tool_ocr_users`)
+  - Task model (mapped to `tool_ocr_tasks`)
+  - TaskFile model (mapped to `tool_ocr_task_files`)
+  - Session model (mapped to `tool_ocr_sessions`)
+  - Configure table prefix in base model
 - [ ] 1.5 Generate Alembic migration
   - Create initial migration for new schema
-  - Test migration script
+  - Test migration script with proper table prefixes
 
 ## 2. Configuration Management
 - [ ] 2.1 Update environment configuration
@@ -30,9 +32,11 @@
   - Add `TASK_RETENTION_DAYS` for auto-cleanup
   - Add `MAX_TASKS_PER_USER` for limits
   - Add `ENABLE_TASK_HISTORY` feature flag
+  - Add `DATABASE_TABLE_PREFIX` = "tool_ocr_"
 - [ ] 2.2 Update Settings class
   - Add external auth settings to `backend/app/core/config.py`
   - Add task management settings
+  - Add database table prefix configuration
   - Add validation for new configuration values
   - Remove old authentication settings