refactor: implement database backend factory for SQLite and MySQL

- Add `get_repository()` factory function to select DB implementation at runtime via DECNET_DB_TYPE env var
- Extract BaseRepository abstract interface from SQLiteRepository
- Update dependencies to use factory-based repository injection
- Add DECNET_DB_TYPE env var support (defaults to sqlite)
- Refactor models and repository base class for cross-dialect compatibility

decnet/web/db/repository.py

@@ -60,6 +60,26 @@ class BaseRepository(ABC):
         """Update a user's password and change the must_change_password flag."""
         pass
 
+    @abstractmethod
+    async def list_users(self) -> list[dict[str, Any]]:
+        """Retrieve all users (caller must strip password_hash before returning to clients)."""
+        pass
+
+    @abstractmethod
+    async def delete_user(self, uuid: str) -> bool:
+        """Delete a user by UUID. Returns True if user was found and deleted."""
+        pass
+
+    @abstractmethod
+    async def update_user_role(self, uuid: str, role: str) -> None:
+        """Update a user's role."""
+        pass
+
+    @abstractmethod
+    async def purge_logs_and_bounties(self) -> dict[str, int]:
+        """Delete all logs, bounties, and attacker profiles. Returns counts of deleted rows."""
+        pass
+
     @abstractmethod
     async def add_bounty(self, bounty_data: dict[str, Any]) -> None:
         """Add a new harvested artifact (bounty) to the database."""
@@ -117,8 +137,23 @@ class BaseRepository(ABC):
         pass
 
     @abstractmethod
-    async def upsert_attacker(self, data: dict[str, Any]) -> None:
-        """Insert or replace an attacker profile record."""
+    async def upsert_attacker(self, data: dict[str, Any]) -> str:
+        """Insert or replace an attacker profile record. Returns the row's UUID."""
+        pass
+
+    @abstractmethod
+    async def upsert_attacker_behavior(self, attacker_uuid: str, data: dict[str, Any]) -> None:
+        """Insert or replace the behavioral/fingerprint row for an attacker."""
+        pass
+
+    @abstractmethod
+    async def get_attacker_behavior(self, attacker_uuid: str) -> Optional[dict[str, Any]]:
+        """Retrieve the behavioral/fingerprint row for an attacker UUID."""
+        pass
+
+    @abstractmethod
+    async def get_behaviors_for_ips(self, ips: set[str]) -> dict[str, dict[str, Any]]:
+        """Bulk-fetch behavior rows keyed by attacker IP (JOIN to attackers)."""
         pass
 
     @abstractmethod