refactor: remove core skill direct loading, skills owned by clawhubadapter only

- Drop skill.NewManager from homed bootstrap; skills dir no longer core-managed
- Remove GetInjectedPrompt system-prompt injection (skills are not first-class)
- Delete internal/skill package, SkillAPI, webui /api/v1/skills, status skills block
- ConfigRegistry: plugin config tables now created only via RegisterDef; arbitrary
  scope Set/Get no longer implicitly creates config_<name> tables (fixes stray
  config_today_task table from SKILL directory name being used as a scope)

internal/sdk/status.go

@@ -21,7 +21,6 @@ type KernelStatus struct {
 	Documents  DocumentStatus   `json:"documents"`
 	TextMemory TextMemoryStatus `json:"text_memory"`
 	Social     SocialStatus     `json:"social"`
-	Skills     SkillsStatus     `json:"skills"`
 
 	LLM LLMStatus `json:"llm"`
 
@@ -72,11 +71,6 @@ type SocialStatus struct {
 	PersonCount int  `json:"person_count"`
 }
 
-type SkillsStatus struct {
-	Available bool     `json:"available"`
-	SkillList []string `json:"skill_list,omitempty"`
-}
-
 type LLMStatus struct {
 	Available bool   `json:"available"`
 	Provider  string `json:"provider,omitempty"`