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/record.go

@@ -0,0 +1,15 @@
+package domain
+
+// RunRecord represents one visible activity item. Scheduled and manual command
+// output is also written to a log file; the in-memory Output copy exists so the
+// latest run can be displayed without reopening the log on every repaint.
+type RunRecord struct {
+	Time    string `yaml:"time"`
+	JobID   int    `yaml:"job_id"`
+	JobName string `yaml:"job_name"`
+	Trigger string `yaml:"trigger,omitempty"`
+	State   string `yaml:"state"`
+	Detail  string `yaml:"detail"`
+	LogFile string `yaml:"log_file,omitempty"`
+	Output  string `yaml:"output,omitempty"`
+}