T1.1: Create src/domain; move Job/RunRecord/Config/JobsFile/StartInTrayArgument

Extracts the five domain types out of src/core/model.go into a new
src/domain package (job.go, record.go, config.go). The unexported
nextDue field is promoted to NextDue so it is accessible from core.
All references across src/core, src/gui, and cmd/gosentry are updated
to use domain.TypeName. src/core/model.go is reduced to a bare package
declaration. Windows and Linux cross-compilation both pass; all tests
remain green.

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

src/domain/config.go

@@ -0,0 +1,25 @@
+package domain
+
+// StartInTrayArgument is written to the Windows Startup shortcut so autostart
+// can keep the scheduler running without flashing the main window. Manual
+// launches omit this flag and open the normal window.
+const StartInTrayArgument = "--start-in-tray"
+
+// Config is stored in gosentry.yaml next to the program. It contains only
+// application-level choices: where to read jobs from, where to write logs, and
+// how the desktop shell should behave.
+type Config struct {
+	JobsDir           string `yaml:"jobs_dir"`
+	LogsDir           string `yaml:"logs_dir"`
+	MaxLogFiles       int    `yaml:"max_log_files"`
+	MaxLogAgeDays     int    `yaml:"max_log_age_days"`
+	StartOnLogin      bool   `yaml:"start_on_login"`
+	KeepRunningInTray bool   `yaml:"keep_running_in_tray"`
+	NotifyOnFailure   bool   `yaml:"notify_on_failure"`
+}
+
+// JobsFile is the on-disk shape of jobs.yaml. Wrapping the slice in a top-level
+// object leaves room for future metadata without breaking the basic file format.
+type JobsFile struct {
+	Jobs []Job `yaml:"jobs"`
+}