domain/job.go: add OverlapPolicy field for per-job run policy

Adds OverlapPolicy field to Job struct with json:"overlap_policy,omitempty"
tag. When empty, the field signals that the job should inherit the global
overlap policy setting from Config. Also updates yamlJob shadow struct to
maintain field-layout equivalence for YAML→JSON import compatibility.

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

src/domain/job.go

@@ -14,4 +14,5 @@ type Job struct {
 	Arguments        string `json:"arguments,omitempty"`
 	StartOnly        bool   `json:"start_only,omitempty"`
 	Enabled          bool   `json:"enabled"`
+	OverlapPolicy    string `json:"overlap_policy,omitempty"`
 }

src/storage/store.go

@@ -44,6 +44,7 @@ type yamlJob struct {
 	Arguments     string `yaml:"arguments,omitempty"`
 	StartOnly     bool   `yaml:"start_only,omitempty"`
 	Enabled       bool   `yaml:"enabled"`
+	OverlapPolicy string `yaml:"overlap_policy,omitempty"`
 }
 
 type yamlJobsFile struct {