Fork of discourse-mlm-daily-summary with extended scheduling, per-user frequency overrides, category scoping, and unsubscribe handling.

This plugin adds a periodic "Activity Update" email to Discourse.

• Sends activity updates as daily or weekly emails.
• Supports a site-wide default frequency and per-user frequency override.
• Can send at a configured time (HH:MM) each day.
• Can restrict included topics to configured categories (including direct subcategories).
• Can auto-enable emails for members of selected groups.
• Supports opt-in or opt-out default behavior.
• Adds an unsubscribe flow and optional unsubscribe link in the email.
• Can optionally use this email type for the admin digest preview/send endpoints.

• A scheduled job runs every 5 minutes in production.
• If mail_daily_summary_at is set, enqueuing starts only after that time each day.
• Daily users are enqueued every day.
• Weekly users are enqueued only on mail_daily_summary_day_of_week (0 = Sunday).
• Users are throttled by per-user send tracking (user_mail_summary_last_sent_at):
  • daily: not sent again within 1 day
  • weekly: not sent again within 7 days

Email content includes topics with posts newer than the selected window:

• daily: posts from the last 24 hours
• weekly: posts from the last 7 days

Base user scope includes real, activated, approved (or staff), non-staged, non-suspended, non-silenced users older than ~24h.

Subscription behavior:

• If mail_daily_summary_enable_as_default = false: users must explicitly enable it.
• If mail_daily_summary_enable_as_default = true: users receive it unless they explicitly disable it.

Frequency behavior:

• Site default is set by mail_daily_summary_frequency.
• Users can override with user_mail_summary_frequency (daily or weekly).
• If a user chooses "Site Default" in preferences, no explicit override is stored.

• mail_daily_summary_enabled
• mail_daily_summary_enable_as_default
• mail_daily_summary_at
• mail_daily_summary_last_run_at (currently not used by enqueue/content window logic)
• mail_daily_summary_debug_mode
• mail_daily_summary_add_unsubscribe_link
• mail_daily_summary_auto_enabled_groups
• mail_daily_summary_enabled_categories
• mail_daily_summary_frequency
• mail_daily_summary_day_of_week
• mail_daily_summary_max_posts_per_topic
• mail_daily_summary_min_excerpt_length
• mail_daily_summary_max_excerpt_length
• mail_daily_summary_preview_uses_daily_summary

In email preferences, users get:

• a checkbox to enable/disable Activity Update emails
• a frequency selector: Site Default, Daily, Weekly

• Uses dedicated daily summary templates in this plugin.
• Subject line changes based on frequency (daily/weekly).
• Excerpts can be constrained with min/max settings.
• mail_daily_summary_max_posts_per_topic limits posts shown per topic when > 0.