chore: remove dead code, deprecate unused plugin APIs (over-engineering audit) (#783)

* chore: remove dead code, deprecate unused plugin APIs (over-engineering audit)

Whole-tree audit. Every symbol was checked against core, the plugin
monorepo and all eight third-party plugins in plugins.json first.

- Deprecate (removal 3.10.0) plugin-facing methods nothing calls:
  LogoDownloader bulk download, ConfigManager backup/secret wrappers,
  APIHelper extras, BackgroundDataService poll API, PluginManager /
  PluginStateManager info readers, and a few CacheManager, FontManager,
  BaseOddsManager, DynamicTeamResolver methods and PluginTestCase.
  plugin_api_usage.py learns their receiver names; DEPRECATIONS doc
  regenerated.
- Remove core-internal dead code: CacheMetrics, Vegas status/stats
  plumbing, sync "new cycle" message (followers ignore unknown types),
  unused operation types, test-only PluginCatalog readers, IPC to_dict
  and ping, _parse_form_value, CacheStrategyProtocol, ErrorAggregator
  callbacks, duplicate web response helpers.
- Web UI: drop never-mounted json-file-manager.js, the example widget,
  utils/error_handler.js, four uncalled PluginAPI methods, and 29
  escapeHtml shims (call window.LEDEscape directly). Public globals,
  BaseWidget and widget names unchanged.
- Remove six one-off scripts (owner decision) and the unused markupsafe
  and pytest-mock pins.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

* fix(web): calendar picker error text goes in a text node, not innerHTML

Same output as the escaped innerHTML it replaces; clears Codacy's
XSS-pattern alerts on the line.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

src/plugin_system/operation_queue.py

@@ -2,7 +2,7 @@
 Plugin operation queue manager.
 
 Serializes plugin operations to prevent conflicts and provides
-status tracking and cancellation support.
+status tracking.
 """
 
 import threading
@@ -25,8 +25,8 @@ class PluginOperationQueue:
     - Serialized execution (one operation at a time)
     - Prevents concurrent operations on same plugin
     - Operation status tracking
-    - Operation cancellation
-    - In-memory history of finished operations
+    - A bounded in-memory history of finished operations, which also caps
+      how many finished operations get_operation_status() remembers
 
     The history is not persisted. The web UI's operation history comes from
     OperationHistory (operation_history.py), which has its own file; a copy
@@ -133,56 +133,6 @@ class PluginOperationQueue:
         with self._lock:
             return self._operations.get(operation_id)
     
-    def cancel_operation(self, operation_id: str) -> bool:
-        """
-        Cancel a pending operation.
-        
-        Args:
-            operation_id: Operation identifier
-        
-        Returns:
-            True if operation was cancelled, False if not found or already running
-        """
-        with self._lock:
-            operation = self._operations.get(operation_id)
-            if not operation:
-                return False
-            
-            if operation.status == OperationStatus.RUNNING:
-                self.logger.warning(
-                    f"Cannot cancel running operation {operation_id}"
-                )
-                return False
-            
-            if operation.status == OperationStatus.PENDING:
-                operation.status = OperationStatus.CANCELLED
-                operation.completed_at = datetime.now()
-                operation.message = "Operation cancelled by user"
-                self._add_to_history(operation)
-                self.logger.info(f"Cancelled operation {operation_id}")
-                return True
-            
-            return False
-    
-    def get_operation_history(self, limit: int = 50) -> List[PluginOperation]:
-        """
-        Get operation history.
-        
-        Args:
-            limit: Maximum number of operations to return
-        
-        Returns:
-            List of operations, sorted by creation time (newest first)
-        """
-        with self._lock:
-            # Sort by creation time (newest first)
-            history = sorted(
-                self._operation_history,
-                key=lambda op: op.created_at,
-                reverse=True
-            )
-            return history[:limit]
-    
     def _start_worker(self) -> None:
         """Start the worker thread that processes operations."""
         if self._worker_thread and self._worker_thread.is_alive():
@@ -207,11 +157,6 @@ class PluginOperationQueue:
                 except queue.Empty:
                     continue
                 
-                # Check if operation was cancelled
-                if operation.status == OperationStatus.CANCELLED:
-                    self._operation_queue.task_done()
-                    continue
-                
                 # Execute operation
                 self._execute_operation(operation)