Fix notification spam bug by persisting notification state across module reloads

[Copilot]

Problem

Users were experiencing constant "Daily goal exceeded!" notifications since the last feature commit. The notifications would appear repeatedly whenever performing common operations like viewing the weekly overview or adding time entries, even when the daily goal notification was configured for oncePerDay = true.

Root Cause

The notification state tracking was stored in a module-local variable that gets reset every time the Lua module is reloaded:

-- This state was lost on module reload
local notification_state = {
    dailyGoal = {
        lastNotification = {}, -- Lost on reload!
        lastRecurringNotification = {},
    },
    coreHours = {
        lastNotification = {},
    },
}

Since checkDailyGoalNotification() is called from within the calculate() function, and calculate() is invoked frequently (weekly overview, adding time, etc.), users would see repeated notifications whenever these operations reset the notification tracking state.

Solution

This PR implements persistent notification state by:

1. Adding state persistence functions:

   • loadNotificationState() - Loads notification state from the JSON data file
   • saveNotificationState() - Saves notification state to the JSON data file

2. Integrating with existing data storage:

   • Notification state is now stored in config_module.obj.content.notificationState
   • State is loaded during plugin initialization after JSON data is read
   • State is automatically saved whenever notifications are triggered or modified

3. Maintaining all existing functionality:

   • Once-per-day notifications continue to work correctly
   • Recurring notifications with configurable intervals still work
   • Mode switching between notification types is preserved
   • Cleanup of old notification entries still functions

Changes Made

• Modified M.init() to load notification state after JSON data is loaded
• Updated notification functions to save state when modified:
  • checkDailyGoalNotification()
  • checkCoreHoursCompliance()
  • _handleModeSwitch()
• Fixed function name typo in cleanup call
• Applied code formatting with stylua

Testing

All existing tests continue to pass (169/169), ensuring no regressions were introduced. The fix specifically addresses the notification spam issue while preserving all existing notification functionality.

Fixes #[issue_number]

Original prompt

---

This section details on the original issue you should resolve

<issue_title>mit letzten commit ein bug</issue_title>
<issue_description>ich bekomme ständig "Daily goal exceeded! ..." seit dem letzten feature-commit.

Berücksichtige die komplette copilot-instructions.md</issue_description>

Comments on the Issue (you are @copilot in this section)

Fixes #129

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