Add best share analysis page, miner column, and UI improvements

- Best share page: hex + binary hash comparison against network target,
  per-bit coloring showing exactly which bits prevented a valid block,
  toggle between network diff at time of finding vs current diff
- Capture best share hash from ckpool logs with one-time backfill
- Persist network difficulty at time of best share for historical accuracy
- Add miner (worker) column to blocks table via coinbase address matching
- Truncate block hashes in table with full hash on hover
- Increase hashrate chart Y-axis to 7 ticks for better readability

api/internal/bitcoind/rpc.go

@@ -222,8 +222,13 @@ type BlockTx struct {
 }
 
 type BlockVout struct {
-	Value float64 `json:"value"`
-	N     int     `json:"n"`
+	Value        float64          `json:"value"`
+	N            int              `json:"n"`
+	ScriptPubKey BlockScriptPubKey `json:"scriptPubKey"`
+}
+
+type BlockScriptPubKey struct {
+	Address string `json:"address"`
 }
 
 // GetBlock returns a verbose-level-2 block decode for the given hash.
@@ -249,6 +254,15 @@ func (b *BlockVerbose2) CoinbaseReward() float64 {
 	return total
 }
 
+// CoinbaseAddress returns the address of the first coinbase output.
+// In ckpool-solo mode this is the miner's BTC payout address.
+func (b *BlockVerbose2) CoinbaseAddress() string {
+	if len(b.Tx) == 0 || len(b.Tx[0].Vout) == 0 {
+		return ""
+	}
+	return b.Tx[0].Vout[0].ScriptPubKey.Address
+}
+
 // NetworkHashPS returns the network hashrate at the given block height.
 // `blocks` is a window (default 120). Pass -1 to use the default.
 func (c *RPC) GetNetworkHashPS(ctx context.Context, blocks, height int) (float64, error) {