refactor(backend): clean up models setup, improve ip utils, add adr docs

- Extract ADR documents for architectural decisions (SQLite, FastAPI, React, APScheduler, Scheduler)
- Refactor setup.py: improve code structure and readability
- Add IP validation utilities with test coverage
- Update frontend components (BanTable, HistoryPage)
- Add pre-commit hooks and CONTRIBUTING.md
- Add .editorconfig for consistent coding standards

backend/app/utils/ip_utils.py

@@ -58,7 +58,9 @@ def normalise_ip(address: str) -> str:
     """Return a normalised string representation of an IP address.
 
     IPv6 addresses are compressed to their canonical short form.
-    IPv4 addresses are returned unchanged.
+    IPv4-mapped IPv6 addresses (e.g. ``::ffff:192.168.1.1``) are converted
+    to their IPv4 equivalent (``192.168.1.1``).
+    Plain IPv4 addresses are returned unchanged.
 
     Args:
         address: A valid IP address string.
@@ -69,7 +71,10 @@ def normalise_ip(address: str) -> str:
     Raises:
         ValueError: If *address* is not a valid IP address.
     """
-    return str(ipaddress.ip_address(address))
+    ip = ipaddress.ip_address(address)
+    if isinstance(ip, ipaddress.IPv6Address) and ip.ipv4_mapped:
+        return str(ip.ipv4_mapped)
+    return str(ip)
 
 
 def normalise_network(cidr: str) -> str: