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/config.go

@@ -5,21 +5,21 @@ package domain
 // 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
+// Config is stored in gosentry.json 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"`
+	JobsDir           string `json:"jobs_dir"`
+	LogsDir           string `json:"logs_dir"`
+	MaxLogFiles       int    `json:"max_log_files"`
+	MaxLogAgeDays     int    `json:"max_log_age_days"`
+	StartOnLogin      bool   `json:"start_on_login,omitempty"`
+	KeepRunningInTray bool   `json:"keep_running_in_tray,omitempty"`
+	NotifyOnFailure   bool   `json:"notify_on_failure,omitempty"`
 }
 
-// JobsFile is the on-disk shape of jobs.yaml. Wrapping the slice in a top-level
+// JobsFile is the on-disk shape of jobs.json. 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"`
+	Jobs []Job `json:"jobs"`
 }