fix: remove unused local variable assignments (pyflakes F841)

Dead assignments removed across src/ and web_interface/:

- background_data_service: drop future= on fire-and-forget executor.submit
- base_classes/baseball: drop font= (all rendering uses self.fonts['time'])
- base_classes/hockey: drop status_short= (never referenced after assignment)
- common/cli: drop game_helper=/config_helper= bindings in import-test block;
  constructors called for instantiation-only validation
- common/display_helper: drop text_width= (x_position uses display_width
  directly); drop draw= in create_error_image (uses _draw_centered_text)
- config_manager: remove dead secrets_content loading block in migration path
  (comment already noted save_config_atomic handles secrets internally)
- display_manager: drop setup_start= (timing was never completed or read)
- font_manager: drop target_path= (catalog uses font_file_path directly);
  drop face=/font= bindings in validate_font (validation by construction —
  TypeError on failure is the signal, not the return value)
- font_test_manager: drop width=/height= (draw_text uses display_manager directly)
- plugin_system/state_reconciliation: drop manager= (only config/disk/state_mgr used)
- plugin_system/store_manager: drop result= on pip install subprocess.run
  (check=True raises on failure; stdout unused)
- web_interface/blueprints/pages_v3: drop main_config_path=""/secrets_config_path=""
  (render_template uses config_manager.get_*_path() inline)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/base_classes/baseball.py

@@ -329,7 +329,6 @@ class Baseball(SportsCore):
             return
         
         series_summary = game.get("series_summary", "")
-        font = self.fonts.get('detail', ImageFont.load_default())
         bbox = draw_overlay.textbbox((0, 0), series_summary, font=self.fonts['time'])
         height = bbox[3] - bbox[1]
         shots_y = (self.display_height - height) // 2

src/base_classes/hockey.py

@@ -77,8 +77,6 @@ class Hockey(SportsCore):
                 away_shots = round(home_team_saves / home_team_saves_per)
             if away_team_saves_per > 0:
                 home_shots = round(away_team_saves / away_team_saves_per)
-            status_short = status["type"].get("shortDetail", "")
-
             if situation and status["type"]["state"] == "in":
                 # Detect scoring events from status detail
                 # status_detail = status["type"].get("detail", "")