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>

configs/ems-config.yaml

@@ -111,7 +111,8 @@ ems:
   recovery_timeout: "1h"             # ignore Shelly state if EMS was down longer
   override_timeout: "1h"             # default lockout when EMS detects external Shelly change
   override_max_import_w: 800         # cancel override immediately if importing more than this (0 = disabled)
-  monitor_only_file: "/etc/ems/monitor-only"  # presence of this file = monitor-only mode active
+  monitor_only_file: "/etc/ems/monitor-only"      # presence of this file = monitor-only mode active
+  ww_boost_disable_file: "/etc/ems/ww-boost-off"  # presence of this file = WW boost disabled
   trip_goal_file: "/var/lib/ems/trip-goal.json"     # persisted active trip goal
   session_log_file: "/var/lib/ems/sessions.jsonl"   # JSONL log of completed charge sessions