feat: Task 4 — paginated banned-IPs section on jail detail page

Backend:
- Add JailBannedIpsResponse Pydantic model (ban.py)
- Add get_jail_banned_ips() service: server-side pagination, optional
  IP substring search, geo enrichment on page slice only (jail_service.py)
- Add GET /api/jails/{name}/banned endpoint with page/page_size/search
  query params, 400/404/502 error handling (routers/jails.py)
- 23 new tests: 13 service tests + 10 router tests (all passing)

Frontend:
- Add JailBannedIpsResponse TS interface (types/jail.ts)
- Add jailBanned endpoint helper (api/endpoints.ts)
- Add fetchJailBannedIps() API function (api/jails.ts)
- Add BannedIpsSection component: Fluent UI DataGrid, debounced search
  (300 ms), prev/next pagination, page-size dropdown, per-row unban
  button, loading spinner, empty state, error MessageBar (BannedIpsSection.tsx)
- Mount BannedIpsSection in JailDetailPage between stats and patterns
- 12 new Vitest tests for BannedIpsSection (all passing)

backend/app/models/ban.py

@@ -306,3 +306,30 @@ class BansByJailResponse(BaseModel):
         description="Jails ordered by ban count descending.",
     )
     total: int = Field(..., ge=0, description="Total ban count in the selected window.")
+
+
+# ---------------------------------------------------------------------------
+# Jail-specific paginated bans
+# ---------------------------------------------------------------------------
+
+
+class JailBannedIpsResponse(BaseModel):
+    """Paginated response for ``GET /api/jails/{name}/banned``.
+
+    Contains only the current page of active ban entries for a single jail,
+    geo-enriched exclusively for the page slice to avoid rate-limit issues.
+    """
+
+    model_config = ConfigDict(strict=True)
+
+    items: list[ActiveBan] = Field(
+        default_factory=list,
+        description="Active ban entries for the current page.",
+    )
+    total: int = Field(
+        ...,
+        ge=0,
+        description="Total matching entries (after applying the search filter).",
+    )
+    page: int = Field(..., ge=1, description="Current page number (1-based).")
+    page_size: int = Field(..., ge=1, description="Number of items per page.")