Add transaction accelerator (prioritisetransaction UI + API)

Full-stack feature for boosting transactions via bitcoind's
prioritisetransaction RPC:

Backend:
- New accelerator package with Accelerate, Cancel, MaxFeerate, List,
  and background Cleanup goroutine (removes confirmed/dropped txs)
- RPC wrappers: GetMempoolEntry, PrioritiseTransaction,
  GetRawMempoolVerbose, IsRPCError helpers
- SQLite boosted_txs table for persistence across restarts
- Revenue impact measured via getblocktemplate before/after comparison
- Hard cap at 2000 sat/vB; MaxFeerate uses fees.base (not modified)
  to ignore our own prior priority adjustments

Frontend:
- Rocket icon in header with 10s jiggle animation
- AcceleratorPage with flame-gradient border, txid input, feerate
  input, "Prioritize above all" button with spinner, boost list with
  cancel buttons, and dismissible error/success messages
- Hash-based routing (#/accelerator)
- SharesBar font size bump

api/cmd/kamado-api/main.go

@@ -18,6 +18,7 @@ import (
 	"syscall"
 	"time"
 
+	"github.com/kamadopool/kamado-api/internal/accelerator"
 	"github.com/kamadopool/kamado-api/internal/bitcoind"
 	"github.com/kamadopool/kamado-api/internal/ckpool"
 	"github.com/kamadopool/kamado-api/internal/config"
@@ -65,10 +66,16 @@ func main() {
 	agg.Store = blockStore
 	agg.MempoolBaseURL = cfg.MempoolBaseURL
 
+	// Transaction accelerator (prioritisetransaction).
+	var accSvc *accelerator.Service
+	if blockStore != nil {
+		accSvc = accelerator.NewService(rpc, blockStore, log)
+	}
+
 	ctx, stop := signal.NotifyContext(context.Background(), syscall.SIGINT, syscall.SIGTERM)
 	defer stop()
 
-	api := httpapi.New(agg, log)
+	api := httpapi.New(agg, accSvc, log)
 
 	// Wire snapshot refreshes into the WebSocket hub so subscribers get
 	// real-time updates without polling.
@@ -130,6 +137,10 @@ func main() {
 	go agg.IngestAttemptEvents(ctx, tailer.Attempts)
 	go agg.IngestLatencyEvents(ctx, tailer.Latencies)
 
+	if accSvc != nil {
+		go accSvc.Cleanup(ctx)
+	}
+
 	srv := &http.Server{
 		Addr:              cfg.ListenAddr,
 		Handler:           api.Handler(),