Record and display winning share difficulty on found blocks

Logmon now captures the share diff from ckpool's "Possible block
solve" line preceding the confirmation and attaches it to the
BlockEvent. Persisted as share_diff alongside height/hash/reward
and rendered as a new column in the dashboard block history.

api/internal/state/blocks.go

@@ -12,11 +12,12 @@ import (
 // data if available. Hash and Reward are populated best-effort via the
 // RPC lookup scheduled right after the log line is seen.
 type BlockRecord struct {
-	Height   int64     `json:"height"`
-	Hash     string    `json:"hash,omitempty"`
-	RewardBT float64   `json:"reward_btc,omitempty"`
-	FoundAt  time.Time `json:"found_at"`
-	Source   string    `json:"source"` // "logmon" for now; "zmq" later
+	Height    int64     `json:"height"`
+	Hash      string    `json:"hash,omitempty"`
+	RewardBT  float64   `json:"reward_btc,omitempty"`
+	FoundAt   time.Time `json:"found_at"`
+	Source    string    `json:"source"` // "logmon" for now; "zmq" later
+	ShareDiff float64   `json:"share_diff,omitempty"`
 }
 
 // IngestBlockEvents reads block events from the tailer and appends them
@@ -31,9 +32,10 @@ func (a *Aggregator) IngestBlockEvents(ctx context.Context, events <-chan logmon
 				return
 			}
 			rec := BlockRecord{
-				Height:  ev.Height,
-				FoundAt: ev.SeenAt,
-				Source:  "logmon",
+				Height:    ev.Height,
+				FoundAt:   ev.SeenAt,
+				Source:    "logmon",
+				ShareDiff: ev.ShareDiff,
 			}
 			// Best-effort enrich with hash + coinbase reward via bitcoind.
 			// We look up the hash from height, then fetch the full block
@@ -56,11 +58,12 @@ func (a *Aggregator) IngestBlockEvents(ctx context.Context, events <-chan logmon
 			}
 			if a.Store != nil {
 				if err := a.Store.InsertBlock(store.Block{
-					Height:   rec.Height,
-					Hash:     rec.Hash,
-					RewardBT: rec.RewardBT,
-					FoundAt:  rec.FoundAt,
-					Source:   rec.Source,
+					Height:    rec.Height,
+					Hash:      rec.Hash,
+					RewardBT:  rec.RewardBT,
+					FoundAt:   rec.FoundAt,
+					Source:    rec.Source,
+					ShareDiff: rec.ShareDiff,
 				}); err != nil {
 					a.Log.Warn("block persist failed", "height", rec.Height, "err", err)
 				}
@@ -114,11 +117,12 @@ func (a *Aggregator) loadPersistedBlocks() {
 	for i := len(rows) - 1; i >= 0; i-- {
 		r := rows[i]
 		recs = append(recs, BlockRecord{
-			Height:   r.Height,
-			Hash:     r.Hash,
-			RewardBT: r.RewardBT,
-			FoundAt:  r.FoundAt,
-			Source:   r.Source,
+			Height:    r.Height,
+			Hash:      r.Hash,
+			RewardBT:  r.RewardBT,
+			FoundAt:   r.FoundAt,
+			Source:    r.Source,
+			ShareDiff: r.ShareDiff,
 		})
 	}
 	a.mu.Lock()