P1.5: drop SuccessExitCodes field and exit-code flexibility

Remove the SuccessExitCodes field from domain.Job and every layer that
read or wrote it: runner/exitcodes.go (deleted), runner.go runStateDetail
simplified to 0=OK / non-zero=Failed, logfile.go, format.go, operations.go,
store.go, job_dialog.go, and jobs_view.go. Tests updated accordingly.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docs/PRE-RELEASE-TASKS.md

@@ -84,7 +84,7 @@ These land together because both edit `domain/job.go` and `storage/store.go`.
 - [x] P1.2 — `writeJSON` + JSON unmarshal
 - [x] P1.3 — `gosentry.json` / `jobs.json` paths; drop pysentry name
 - [x] P1.4 — One-time YAML import
-- [ ] P1.5 — Remove `SuccessExitCodes` across code
+- [x] P1.5 — Remove `SuccessExitCodes` across code
 - [ ] P1.6 — Update storage/runner/format tests + TESTS.md
 
 ### Phase 2 — PySentry legacy removal