Add WW boost enable/disable toggle (persistent flag file)

In summer the WW boost interferes with car charging priority.
A new ⛔/✅ toggle on the WW consumer card persists to
/etc/ems/ww-boost-off (presence = disabled, absence = enabled).

- config: ww_boost_disable_file flag file path
- main: wwBoostDisabled mode, wwBoostToggleHandler, runCycle skips
  computeWWBoost when disabled
- status: WWBoostDisabled in pageData, toggle button in WW card
  showing ⛔ Boost aus / ✅ Boost ein depending on state

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

internal/config/config.go

@@ -167,6 +167,7 @@ type EMSConfig struct {
 	OverrideTimeout    string  `yaml:"override_timeout"`
 	OverrideMaxImportW float64 `yaml:"override_max_import_w"` // cancel override if grid import exceeds this (0 = disabled)
 	MonitorOnlyFile    string  `yaml:"monitor_only_file"`     // flag file path: presence = monitor-only mode active
+	WWBoostDisableFile string  `yaml:"ww_boost_disable_file"` // flag file path: presence = WW boost disabled
 	TripGoalFile       string  `yaml:"trip_goal_file"`        // persisted active trip goal
 	SessionLogFile     string  `yaml:"session_log_file"`      // JSONL log of completed charge sessions
 }