P1.1: swap yaml struct tags for json in domain types

Replace yaml:"…" tags with json:"…" on Job, Config, and JobsFile.
Add omitempty to bool fields in Config that previously lacked it.
Update comments to reference .json filenames.

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

src/domain/job.go

@@ -1,18 +1,18 @@
 package domain
 
 // Job is the user-visible scheduled command. It contains only durable
-// configuration: every field is persisted to jobs.yaml. Transient execution
+// configuration: every field is persisted to jobs.json. Transient execution
 // state (last run, next run, command output, in-memory activity) lives in a
 // separate JobRuntime so the jobs file stays a clean, hand-editable record of
 // configuration and never mixes in process-lifetime bookkeeping.
 type Job struct {
-	ID               int    `yaml:"id"`
-	Name             string `yaml:"name"`
-	Folder           string `yaml:"folder,omitempty"`
-	Schedule         string `yaml:"schedule"`
-	Command          string `yaml:"command"`
-	Arguments        string `yaml:"arguments,omitempty"`
-	SuccessExitCodes string `yaml:"success_exit_codes,omitempty"`
-	StartOnly        bool   `yaml:"start_only,omitempty"`
-	Enabled          bool   `yaml:"enabled"`
+	ID               int    `json:"id"`
+	Name             string `json:"name"`
+	Folder           string `json:"folder,omitempty"`
+	Schedule         string `json:"schedule"`
+	Command          string `json:"command"`
+	Arguments        string `json:"arguments,omitempty"`
+	SuccessExitCodes string `json:"success_exit_codes,omitempty"`
+	StartOnly        bool   `json:"start_only,omitempty"`
+	Enabled          bool   `json:"enabled"`
 }