fix(kernel,server,tui,inference): generic resource gauge + F-002/F-003/F-004

- generic SystemResourceProbe: owner-agnostic /proc/meminfo system RAM
  overlaid on the vendor GPU probe, wired on both managed and static paths
  so the VRAM/GPU/RAM gauge renders with an external llama-server (was dormant)
- F-002: classify provider 4xx (e.g. llama.cpp 400) as terminal, not retryable
  (except 408/429); stops retrying deterministic request failures to exhaustion
- F-003: FileSystemPromptLoader expands leading ~ / ~/ to user home
- F-004: map InferenceFailedEvent + RetryAttemptedEvent to new
  ServerMessage.InferenceFailed / RetryAttempted, decoded+rendered in tui-go;
  ArtifactContentStoredEvent explicitly mapped to null (internal, no warn)
- tests: tilde expansion, SystemResourceProbe (static/managed/fail-soft)

apps/tui-go/internal/app/view.go

@@ -117,8 +117,11 @@ func (m Model) gaugeText() string {
 	if m.gpuUtil != nil {
 		parts = append(parts, "GPU "+itoa(*m.gpuUtil)+"%")
 	}
+	if m.sysRamUsedMB != nil && m.sysRamTotalMB != nil {
+		parts = append(parts, "RAM "+itoa(int(*m.sysRamUsedMB))+"/"+itoa(int(*m.sysRamTotalMB))+"M")
+	}
 	if m.ramMB != nil {
-		parts = append(parts, "RAM "+itoa(int(*m.ramMB))+"M")
+		parts = append(parts, "proc "+itoa(int(*m.ramMB))+"M")
 	}
 	return strings.Join(parts, " ")
 }