domain/config.go + app: persist global pause state across restarts (T4.1, T4.2)

Add Config.Paused bool so the scheduler's paused flag survives a restart.
SetGlobalPause now writes the flag into store.Config and calls SaveConfig;
NewService seeds s.paused from Config.Paused before computing first next-run
times, so jobs show "Scheduler paused" immediately at startup when paused.
Also add Paused to the yamlConfig shadow struct to keep the direct conversion
from domain.Config valid until the YAML import path is dropped in T6.3.

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

src/domain/config.go

@@ -40,6 +40,7 @@ type Config struct {
 	NotifyOnFailure   bool          `json:"notify_on_failure,omitempty"`
 	ExecutionMode     ExecutionMode `json:"execution_mode,omitempty"`
 	OverlapPolicy     OverlapPolicy `json:"overlap_policy,omitempty"`
+	Paused            bool          `json:"paused,omitempty"`
 }
 
 // JobsFile is the on-disk shape of jobs.json. Wrapping the slice in a top-level