Refactor ban management with domain models and mappers

- Add ban domain model for core business logic separation
- Implement mapper pattern for DTO/domain conversions
- Update ban service with new domain-driven approach
- Refactor router endpoints to use new architecture
- Add comprehensive mapper tests
- Update documentation with architecture changes

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

backend/app/models/ban_domain.py

@@ -0,0 +1,110 @@
+"""Ban domain models (DTOs).
+
+Internal domain-focused models used by ban_service. These represent the
+business domain layer and are independent of HTTP response shapes.
+
+Response models are defined in `app.models.ban` and mappers convert domain
+models to response models at the router boundary.
+"""
+
+from __future__ import annotations
+
+from dataclasses import dataclass
+from typing import Literal
+
+# Domain-specific ban origin type
+BanOriginDomain = Literal["blocklist", "selfblock"]
+
+
+@dataclass(frozen=True)
+class DomainActiveBan:
+    """A currently active ban entry (domain model).
+
+    This is the service-layer representation, independent of API response shape.
+    """
+
+    ip: str
+    jail: str
+    banned_at: str | None = None
+    expires_at: str | None = None
+    ban_count: int = 1
+    country: str | None = None
+
+
+@dataclass(frozen=True)
+class DomainActiveBanList:
+    """List of currently active bans (domain model)."""
+
+    bans: list[DomainActiveBan]
+    total: int
+
+
+@dataclass(frozen=True)
+class DomainDashboardBanItem:
+    """A single row in the dashboard ban-list table (domain model).
+
+    Populated from the fail2ban database and enriched with geo data.
+    """
+
+    ip: str
+    jail: str
+    banned_at: str
+    service: str | None = None
+    country_code: str | None = None
+    country_name: str | None = None
+    asn: str | None = None
+    org: str | None = None
+    ban_count: int = 1
+    origin: BanOriginDomain = "selfblock"
+
+
+@dataclass(frozen=True)
+class DomainDashboardBanList:
+    """Paginated dashboard ban-list (domain model)."""
+
+    items: list[DomainDashboardBanItem]
+    total: int
+    page: int
+    page_size: int
+
+
+@dataclass(frozen=True)
+class DomainBansByCountry:
+    """Bans aggregated by country (domain model)."""
+
+    countries: dict[str, int]
+    country_names: dict[str, str]
+    items: list[DomainDashboardBanItem]
+    total: int
+
+
+@dataclass(frozen=True)
+class DomainBanTrendBucket:
+    """A single time bucket in the ban trend series (domain model)."""
+
+    timestamp: str
+    count: int
+
+
+@dataclass(frozen=True)
+class DomainBanTrend:
+    """Ban trend data over time (domain model)."""
+
+    buckets: list[DomainBanTrendBucket]
+    bucket_size: str
+
+
+@dataclass(frozen=True)
+class DomainJailBanCount:
+    """Ban count for a single jail (domain model)."""
+
+    jail: str
+    count: int
+
+
+@dataclass(frozen=True)
+class DomainBansByJail:
+    """Bans aggregated by jail (domain model)."""
+
+    jails: list[DomainJailBanCount]
+    total: int