Fixes#6746
API-driven issue updates (PUT update, PUT create-via-upsert, PATCH) were
missing `model_activity.delay()` calls, so webhooks were never dispatched
for changes made through the API. The web UI paths already include these
calls (e.g. in `post()` at L475), but the `put()` and `partial_update()`
methods only called `issue_activity.delay()`.
This adds `model_activity.delay()` immediately after each existing
`issue_activity.delay()` in these three code paths, using the same
signature as the existing call in `post()`.
Tested on Plane CE v1.2.1 self-hosted: API PATCH triggers
`webhook_send_task` in the Celery worker, confirming webhook delivery.
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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