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/protocol/protocol.go

@@ -26,6 +26,8 @@ const (
 	TypeInferenceStarted = "inference.started"
 	TypeInferenceDone    = "inference.completed"
 	TypeInferenceTimeout = "inference.timed_out"
+	TypeInferenceFailed  = "inference.failed"
+	TypeInferenceRetry   = "inference.retry"
 	TypeToolStarted      = "tool.started"
 	TypeToolCompleted    = "tool.completed"
 	TypeToolFailed       = "tool.failed"
@@ -77,6 +79,11 @@ type ServerMessage struct {
 	Outcome       string  `json:"outcome"`       // approval.resolved: APPROVED | REJECTED | AUTO_APPROVED
 	WorkspaceRoot string  `json:"workspaceRoot"` // session.workspace_bound: the bound cwd
 
+	// inference.retry
+	AttemptNumber int    `json:"attemptNumber"`
+	MaxAttempts   int    `json:"maxAttempts"`
+	FailureReason string `json:"failureReason"`
+
 	SteeringEmitted bool  `json:"steeringEmitted"`
 	OccurredAt      int64 `json:"occurredAt"`
 	ElapsedMs       int64 `json:"elapsedMs"`
@@ -99,6 +106,8 @@ type ServerMessage struct {
 	GpuMemoryTotalMb  *int64 `json:"gpuMemoryTotalMb"`
 	GpuUtilizationPct *int   `json:"gpuUtilizationPct"`
 	ProcessRssMb      *int64 `json:"processRssMb"`
+	SystemRamUsedMb   *int64 `json:"systemRamUsedMb"`
+	SystemRamTotalMb  *int64 `json:"systemRamTotalMb"`
 
 	State          *SessionStateDto   `json:"state"`
 	RiskSummary    *RiskSummaryDto    `json:"riskSummary"`
@@ -209,6 +218,7 @@ func (m ServerMessage) IsEventBearing() bool {
 		TypeSessionCompleted, TypeSessionFailed,
 		TypeStageStarted, TypeStageCompleted, TypeStageFailed,
 		TypeInferenceStarted, TypeInferenceDone, TypeInferenceTimeout,
+		TypeInferenceFailed, TypeInferenceRetry,
 		TypeToolStarted, TypeToolCompleted, TypeToolFailed, TypeToolRejected,
 		TypeToolAssessed,
 		TypeApprovalRequired, TypeApprovalResolved, TypeWorkspaceBound, TypeArtifactCreated,