Complete tasks 1-5: UI cleanup, pie chart fix, log path allowlist, activation hardening

Task 1: Remove ActiveBansSection from JailsPage
- Delete buildBanColumns, fmtTimestamp, ActiveBansSection
- Remove Dialog/Delete/Dismiss imports, ActiveBan type
- Update JSDoc to reflect three sections

Task 2: Remove JailDistributionChart from Dashboard
- Delete import and JSX block from DashboardPage.tsx

Task 3: Fix transparent pie chart (TopCountriesPieChart)
- Add Cell import and per-slice <Cell fill={slice.fill}> children inside <Pie>
- Suppress @typescript-eslint/no-deprecated (recharts v3 types)

Task 4: Allow /config/log as safe log prefix
- Add '/config/log' to _SAFE_LOG_PREFIXES in config_service.py
- Update error message to list both allowed directories

Task 5: Block jail activation on missing filter/logpath
- activate_jail refuses to proceed when filter/logpath issues found
- ActivateJailDialog treats all validation issues as blocking
- Trigger immediate _run_probe after activation in config router
- /api/health now reports fail2ban online/offline from cached probe
- Add TestActivateJailBlocking tests; fix existing tests to mock validation

backend/app/services/config_file_service.py

@@ -1136,6 +1136,25 @@ async def activate_jail(
             warnings=warnings,
         )
 
+    # Block activation on critical validation failures (missing filter or logpath).
+    blocking = [i for i in validation_result.issues if i.field in ("filter", "logpath")]
+    if blocking:
+        log.warning(
+            "jail_activation_blocked",
+            jail=name,
+            issues=[f"{i.field}: {i.message}" for i in blocking],
+        )
+        return JailActivationResponse(
+            name=name,
+            active=False,
+            fail2ban_running=True,
+            validation_warnings=warnings,
+            message=(
+                f"Jail {name!r} cannot be activated: "
+                + "; ".join(i.message for i in blocking)
+            ),
+        )
+
     overrides: dict[str, Any] = {
         "bantime": req.bantime,
         "findtime": req.findtime,