feat(database): Add comprehensive database initialization module

- Add src/server/database/init.py with complete initialization framework
  * Schema creation with idempotent table generation
  * Schema validation with detailed reporting
  * Schema versioning (v1.0.0) and migration support
  * Health checks with connectivity monitoring
  * Backup functionality for SQLite databases
  * Initial data seeding framework
  * Utility functions for database info and migration guides

- Add comprehensive test suite (tests/unit/test_database_init.py)
  * 28 tests covering all functionality
  * 100% test pass rate
  * Integration tests and error handling

- Update src/server/database/__init__.py
  * Export new initialization functions
  * Add schema version and expected tables constants

- Fix syntax error in src/server/models/anime.py
  * Remove duplicate import statement

- Update instructions.md
  * Mark database initialization task as complete

Features:
- Automatic schema creation and validation
- Database health monitoring
- Backup creation with timestamps
- Production-ready with Alembic migration guidance
- Async/await support throughout
- Comprehensive error handling and logging

Test Results: 69/69 database tests passing (100%)

src/server/database/__init__.py

@@ -23,6 +23,19 @@ Usage:
 
 from src.server.database.base import Base
 from src.server.database.connection import close_db, get_db_session, init_db
+from src.server.database.init import (
+    CURRENT_SCHEMA_VERSION,
+    EXPECTED_TABLES,
+    check_database_health,
+    create_database_backup,
+    create_database_schema,
+    get_database_info,
+    get_migration_guide,
+    get_schema_version,
+    initialize_database,
+    seed_initial_data,
+    validate_database_schema,
+)
 from src.server.database.models import (
     AnimeSeries,
     DownloadQueueItem,
@@ -37,14 +50,29 @@ from src.server.database.service import (
 )
 
 __all__ = [
+    # Base and connection
     "Base",
     "get_db_session",
     "init_db",
     "close_db",
+    # Initialization functions
+    "initialize_database",
+    "create_database_schema",
+    "validate_database_schema",
+    "get_schema_version",
+    "seed_initial_data",
+    "check_database_health",
+    "create_database_backup",
+    "get_database_info",
+    "get_migration_guide",
+    "CURRENT_SCHEMA_VERSION",
+    "EXPECTED_TABLES",
+    # Models
     "AnimeSeries",
     "Episode",
     "DownloadQueueItem",
     "UserSession",
+    # Services
     "AnimeSeriesService",
     "EpisodeService",
     "DownloadQueueService",