[IMP] helpdesk_user_default_ticket_team: document behaviour and convert README to markdown

- Add docstrings to ``_compute_user_id``, ``create`` and
  ``_define_user_id`` and clarify the inline comments describing the
  team-leader fallback rules.
- Convert ``README.rst`` to ``README.md``, documenting usage, the
  graceful handling of partners without a linked user, and how to run
  the test suite.

helpdesk_user_default_ticket_team/README.md

@@ -0,0 +1,92 @@
+# helpdesk_user_default_ticket_team
+
+Automate ticket team attribution when a ticket is created by a portal user.
+
+This module extends the `helpdesk_mgmt` module by allowing to configure a
+default helpdesk team per user. It provides:
+
+- A new `default_helpdesk_ticket_team_id` field on the user form, located in
+  the Preferences tab.
+- Automatic team assignment when a ticket is created:
+  - If the ticket has no team assigned and has a linked partner.
+  - The module looks up the user associated with the partner. A partner with
+    no linked user (e.g. a plain contact) is handled gracefully and left
+    untouched.
+  - If the user has a default helpdesk team configured, it is automatically
+    assigned to the ticket.
+  - If the assigned team has a default project, the ticket is also linked to
+    that project.
+- Automatic user assignment when a team is selected:
+  - When a team is set or changed on a ticket, if the current assigned user
+    is not a member of that team, the team leader (`team_id.user_id`) is
+    automatically assigned instead.
+  - If the team has no leader configured, the assigned user is left unchanged
+    (to avoid creating unassigned tickets).
+
+This is particularly useful for multi-company or multi-team environments where
+portal users should always have their tickets routed to a specific team.
+
+# Installation
+
+Use Odoo normal module installation procedure to install
+`helpdesk_user_default_ticket_team`.
+
+This module depends on:
+
+- `helpdesk_mgmt`: provides the base helpdesk ticket functionality.
+- `helpdesk_mgmt_project`: provides the link between tickets and projects.
+
+# Usage
+
+1. Open a user form (Settings > Users & Companies > Users).
+2. In the **Preferences** tab, set the **Default Helpdesk Team** field.
+3. When that user (through its linked partner) creates a ticket without an
+   explicit team, the ticket is automatically routed to the configured team,
+   its default project, and the team leader.
+
+# Testing
+
+Automated tests live in `tests/test_helpdesk_ticket.py` and cover:
+
+- The `_define_user_id` decision logic (no team, no current user, user not in
+  team, user in team, team without leader).
+- The `create` auto-assignment (with/without partner, with/without default
+  team, explicit team not overridden, partner without linked user, batch
+  creation).
+- The `_compute_user_id` recomputation when the team changes.
+- The full portal creation flow (team + project + user) and the presence of
+  the `default_helpdesk_ticket_team_id` field on `res.users`.
+
+Run them with:
+
+```
+odoo-bin -d <db> --test-enable --stop-after-init \
+    -i helpdesk_user_default_ticket_team
+```
+
+# Known issues / Roadmap
+
+None yet.
+
+# Bug Tracker
+
+Bugs are tracked on [our issues website](https://git.elabore.coop/Elabore/helpdesk-tools/issues).
+In case of trouble, please check there if your issue has already been
+reported. If you spotted it first, help us smashing it by providing a
+detailed and welcomed feedback.
+
+# Credits
+
+## Contributors
+
+- Stéphan Sainléger - [Email](mailto:stephan.sainleger@elabore.coop)
+
+## Funders
+
+The development of this module has been financially supported by:
+
+- Elabore (https://elabore.coop)
+
+## Maintainer
+
+This module is maintained by Elabore.