Remote xcresult ingestion now stores complete test results instead of silently dropping cases

Fixes a bug in remote xcresult processing where test runs sometimes stored only a partial, unpredictable set of test cases. The root cause was a missing database permission for the processor role to read webhook endpoints, which caused ingestion to abort mid-run and left duplicate device entries. Processor grants are now applied automatically at migration time, and the webhook_endpoints table is readable, so re-uploading or re-processing a run now produces a full, deterministic result.