Add smart Taskist assignment SLA push flow

.gitignore

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+node_modules/
+frontend/node_modules/
+
+__pycache__/
+*.py[cod]
+*$py.class
+
+.ruff_cache/
+.pytest_cache/
+.mypy_cache/
+
+.DS_Store
+Thumbs.db
+
+.env
+.env.*
+!.env.example

docs/smart-taskist-roadmap.md

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+# Smart Taskist Roadmap
+
+Taskist can become an activity layer over ERPNext documents, not only a Project Task UI.
+
+## Source-Linked Tasks
+
+Taskist should use ERPNext `Task` as the single work item, whether or not it belongs to a Project.
+
+- Source document: any DocType, such as Purchase Order, Sales Order, Issue, Lead, Payment Entry, or Issue.
+- Assigned user: the user responsible for the next action, copied from the source document assignment.
+- Task state: Open, Working, Pending Review, Completed, Cancelled.
+- Deep link: every source-linked Task opens the originating document.
+- Project remains optional.
+
+## Document Assignment Automation
+
+When a supported document is assigned through Frappe assignment, Taskist should create or update a normal ERPNext Task.
+
+Suggested first slice:
+
+- Listen to `ToDo` creation/update events where `reference_type` and `reference_name` point to a business document.
+- Create a source-linked Task for the assigned user.
+- Mark the Task complete when the related `ToDo` is closed.
+- Let users complete the Task from Taskist, then close/update the linked `ToDo`.
+
+## SLA Engine
+
+Create a `Taskist SLA Rule` DocType that defines how long a document or activity should take.
+
+Recommended fields:
+
+- Rule name and enabled flag.
+- Reference DocType.
+- Conditions JSON, using Frappe filter syntax.
+- Start event: document creation, assignment, status change, submitted, or custom field transition.
+- Stop event: completed activity, document status, workflow state, submitted/cancelled, or custom field transition.
+- Duration target in minutes/hours/days.
+- Business calendar, holiday list, and working hours.
+- Escalation recipients and notification channels.
+
+Runtime records should be stored separately in `Taskist SLA Tracker`, one per matched document or source-linked Task.
+
+Initial implementation:
+
+- SLA rules target a source DocType.
+- Conditions are stored as optional JSON filters.
+- Source-linked Tasks get a tracker when they match an enabled rule.
+- Trackers compute start time, warning time, and due time.
+- The hourly scheduler evaluates open trackers.
+- Warning and breach events can send push notifications.
+
+## Notifications
+
+Push notifications should be one delivery channel beside email and in-app realtime updates.
+
+Useful notification events:
+
+- New assignment.
+- SLA warning threshold reached.
+- SLA breached.
+- Activity completed.
+- Activity sent back for review.
+- Comment or attachment added on an assigned activity.
+
+The initial push implementation stores browser subscriptions and exposes a reusable backend sender. SLA and activity events can call `taskist.push.send_push_to_user`.