feat: añadir campo Message/Template/Prompt a ScheduledAction y dependencia cron

Se añaden tres campos nuevos a ScheduledAction en internal/config/schema.go:
- Message: texto inline para send_message
- Template: ruta a archivo .md para send_message o llm_prompt
- Prompt: texto inline del prompt para llm_prompt

Se agrega github.com/robfig/cron/v3 v3.0.1 como dependencia.
No hay cambios de ruptura: los campos son opcionales y el schema existente
sigue siendo compatible.

go.mod

@@ -41,6 +41,7 @@ require (
 	github.com/petermattis/goid v0.0.0-20240813172612-4fcff4a6cae7 // indirect
 	github.com/remyoudompheng/bigfft v0.0.0-20230129092748-24d4a6f8daec // indirect
 	github.com/rivo/uniseg v0.4.7 // indirect
+	github.com/robfig/cron/v3 v3.0.1 // indirect
 	github.com/rs/zerolog v1.33.0 // indirect
 	github.com/spf13/cast v1.7.1 // indirect
 	github.com/spf13/pflag v1.0.5 // indirect

go.sum

@@ -79,6 +79,8 @@ github.com/remyoudompheng/bigfft v0.0.0-20230129092748-24d4a6f8daec/go.mod h1:qq
 github.com/rivo/uniseg v0.2.0/go.mod h1:J6wj4VEh+S6ZtnVlnTBMWIodfgj8LQOQFoIToxlJtxc=
 github.com/rivo/uniseg v0.4.7 h1:WUdvkW8uEhrYfLC4ZzdpI2ztxP1I582+49Oc5Mq64VQ=
 github.com/rivo/uniseg v0.4.7/go.mod h1:FN3SvrM+Zdj16jyLfmOkMNblXMcoc8DfTHruCPUcx88=
+github.com/robfig/cron/v3 v3.0.1 h1:WdRxkvbJztn8LMz/QEvLN5sBU+xKpSqwwUO1Pjr4qDs=
+github.com/robfig/cron/v3 v3.0.1/go.mod h1:eQICP3HwyT7UooqI/z+Ov+PtYAWygg1TEWWzGIFLtro=
 github.com/rogpeppe/go-internal v1.9.0 h1:73kH8U+JUqXU8lRuOHeVHaa/SZPifC7BkcraZVejAe8=
 github.com/rogpeppe/go-internal v1.9.0/go.mod h1:WtVeX8xhTBvf0smdhujwtBcq4Qrzq/fJaraNFVN+nFs=
 github.com/rs/xid v1.5.0/go.mod h1:trrq9SKmegXys3aeAKXMUTdJsYXVwGY3RLcfgqegfbg=

internal/config/schema.go

@@ -340,6 +340,11 @@ type ScheduledAction struct {
 	Target  string `yaml:"target"`
 	Command string `yaml:"command"`
 	Script  string `yaml:"script"`
+
+	// Phase 1: send_message and llm_prompt fields
+	Message  string `yaml:"message"`  // inline text for send_message
+	Template string `yaml:"template"` // path to .md file for send_message
+	Prompt   string `yaml:"prompt"`   // inline prompt text for llm_prompt
 }
 
 type FailureAction struct {