feat: materialize open supervision topics as Focus Queue tasks

[dholbach]

Summary

• SupervisionItem (existing per-client supervision agenda model, with its own cross-client /supervision/ queue at supervision_queue) fits the same materialize-and-reconcile pattern already used for missing session logs and unpaid/unsent invoices.
• sync_focus_queue_tasks now also creates one Task per open (status=offen) SupervisionItem, auto-closed when the item is marked besprochen (existing toggle on the client detail page / supervision queue) — reusing the existing generic _sync_object_tasks helper, no new plumbing.
• related_object_url gains a supervisionitem branch linking to the client detail page (client_detail), since SupervisionItem has no page of its own.
• Closes the "supervision" half of Focus Queue: design recurring_review task type (periodic case/progress review) #280 — task_type=SUPERVISION was previously a dead enum value nothing ever assigned. RECURRING_REVIEW remains open, tracked separately (needs its own design — periodic case/progress review, not yet scoped).

Design notes

• Task titles use the client code only, never SupervisionItem.content — that field is Fernet-encrypted specifically because it can hold sensitive clinical material, so it must stay out of a plaintext title (same rule the command already follows for the other materialized types).
• Like the other three materialized types, completing the Task in the Focus Queue does not flip SupervisionItem.status back to besprochen — the sync only reconciles source → task, not the reverse. Pre-existing asymmetry, not new here.
• /supervision/ (the dedicated cross-client queue) is untouched and stays as the detailed per-client view; the Focus Queue now just also surfaces the same open items in the unified "what needs doing" list.

Test plan

• ./dev.py test my_practice.tests.test_sync_focus_queue_tasks my_practice.tests.test_practice_todo my_practice.tests.test_views_focus_queue — 63 tests pass
• ./dev.py lint passes

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