Implement tasks 1-3: sidebar order, jail activation rollback, pie chart colors

Task 1: Move Configuration to last position in sidebar NAV_ITEMS

Task 2: Add automatic rollback when jail activation fails
- Back up .local override file before writing
- Restore original file (or delete) on reload failure, health-check
  failure, or jail not appearing post-reload
- Return recovered=True/False in JailActivationResponse
- Show warning/critical banner in ActivateJailDialog based on recovery
- Add _restore_local_file_sync and _rollback_activation_async helpers
- Add 3 new tests: rollback on reload failure, health-check failure,
  and double failure (recovered=False)

Task 3: Color pie chart legend labels to match their slice color
- legendFormatter now returns ReactNode with span style={{ color }}
- Import LegendPayload from recharts/types/component/DefaultLegendContent

backend/app/models/config.py

@@ -873,6 +873,16 @@ class JailActivationResponse(BaseModel):
         default_factory=list,
         description="Non-fatal warnings from the pre-activation validation step.",
     )
+    recovered: bool | None = Field(
+        default=None,
+        description=(
+            "Set when activation failed after writing the config file.  "
+            "``True`` means the system automatically rolled back the change and "
+            "restarted fail2ban.  ``False`` means the rollback itself also "
+            "failed and manual intervention is required.  ``None`` when "
+            "activation succeeded or failed before the file was written."
+        ),
+    )
 
 
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