Remove stats from .runtime/*.json observable state (gt-lfi2d)

Remove Stats fields from witness and refinery types that tracked
observable metrics (total counts, today counts). These are now
handled by the activity stream/beads system instead.

Removed:
- WitnessStats type and Stats field from Witness
- RefineryStats type and Stats field from Refinery
- LastCheckAt field from Witness
- Stats display from gt witness status
- Stats display from gt refinery status
- Stats increment code from refinery.completeMR()

Kept minimal process state:
- RigName, State, PID, StartedAt (both)
- MonitoredPolecats, Config, SpawnedIssues (witness)
- CurrentMR, PendingMRs, LastMergeAt (refinery)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

internal/refinery/types.go

@@ -44,9 +44,6 @@ type Refinery struct {
 
 	// LastMergeAt is when the last successful merge happened.
 	LastMergeAt *time.Time `json:"last_merge_at,omitempty"`
-
-	// Stats contains cumulative statistics.
-	Stats RefineryStats `json:"stats"`
 }
 
 // MergeRequest represents a branch waiting to be merged.
@@ -150,24 +147,6 @@ func DefaultMergeConfig() MergeConfig {
 	}
 }
 
-// RefineryStats contains cumulative refinery statistics.
-type RefineryStats struct {
-	// TotalMerged is the total number of successful merges.
-	TotalMerged int `json:"total_merged"`
-
-	// TotalFailed is the total number of failed merges.
-	TotalFailed int `json:"total_failed"`
-
-	// TotalSkipped is the total number of skipped MRs.
-	TotalSkipped int `json:"total_skipped"`
-
-	// TodayMerged is the number of merges today.
-	TodayMerged int `json:"today_merged"`
-
-	// TodayFailed is the number of failures today.
-	TodayFailed int `json:"today_failed"`
-}
-
 // QueueItem represents an item in the merge queue for display.
 type QueueItem struct {
 	Position  int       `json:"position"`