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/internal/httpapi/accelerate.go

@@ -0,0 +1,106 @@
+package httpapi
+
+import (
+	"encoding/json"
+	"net/http"
+	"regexp"
+
+	"github.com/kamadopool/kamado-api/internal/bitcoind"
+	"github.com/kamadopool/kamado-api/internal/store"
+)
+
+var txidRE = regexp.MustCompile(`^[0-9a-fA-F]{64}$`)
+
+type accelerateReq struct {
+	Txid       string  `json:"txid"`
+	FeerateVB  float64 `json:"fee_rate_satvb"`
+}
+
+type cancelReq struct {
+	Txid string `json:"txid"`
+}
+
+func (s *Server) accelerate(w http.ResponseWriter, r *http.Request) {
+	if s.Acc == nil {
+		writeJSON(w, http.StatusServiceUnavailable, map[string]any{"error": "accelerator not available (no store)"})
+		return
+	}
+	var req accelerateReq
+	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+		writeJSON(w, http.StatusBadRequest, map[string]any{"error": "invalid JSON: " + err.Error()})
+		return
+	}
+	if !txidRE.MatchString(req.Txid) {
+		writeJSON(w, http.StatusBadRequest, map[string]any{"error": "invalid txid: must be 64 hex characters"})
+		return
+	}
+	if req.FeerateVB <= 0 {
+		writeJSON(w, http.StatusBadRequest, map[string]any{"error": "fee_rate_satvb must be positive"})
+		return
+	}
+	if req.FeerateVB > 2000 {
+		writeJSON(w, http.StatusBadRequest, map[string]any{"error": "fee_rate_satvb cannot exceed 2000 sat/vB"})
+		return
+	}
+
+	result, err := s.Acc.Accelerate(r.Context(), req.Txid, req.FeerateVB)
+	if err != nil {
+		status := http.StatusInternalServerError
+		if bitcoind.IsRPCError(err, -5) {
+			status = http.StatusNotFound
+		}
+		writeJSON(w, status, map[string]any{"error": bitcoind.RPCErrorMessage(err)})
+		return
+	}
+	writeJSON(w, http.StatusOK, result)
+}
+
+func (s *Server) accelerateCancel(w http.ResponseWriter, r *http.Request) {
+	if s.Acc == nil {
+		writeJSON(w, http.StatusServiceUnavailable, map[string]any{"error": "accelerator not available"})
+		return
+	}
+	var req cancelReq
+	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+		writeJSON(w, http.StatusBadRequest, map[string]any{"error": "invalid JSON: " + err.Error()})
+		return
+	}
+	if !txidRE.MatchString(req.Txid) {
+		writeJSON(w, http.StatusBadRequest, map[string]any{"error": "invalid txid"})
+		return
+	}
+	if err := s.Acc.Cancel(r.Context(), req.Txid); err != nil {
+		writeJSON(w, http.StatusBadRequest, map[string]any{"error": err.Error()})
+		return
+	}
+	writeJSON(w, http.StatusOK, map[string]any{"ok": true})
+}
+
+func (s *Server) accelerateMax(w http.ResponseWriter, r *http.Request) {
+	if s.Acc == nil {
+		writeJSON(w, http.StatusServiceUnavailable, map[string]any{"error": "accelerator not available"})
+		return
+	}
+	rate, err := s.Acc.MaxFeerate(r.Context())
+	if err != nil {
+		writeJSON(w, http.StatusInternalServerError, map[string]any{"error": err.Error()})
+		return
+	}
+	writeJSON(w, http.StatusOK, map[string]any{"max_feerate_satvb": rate})
+}
+
+func (s *Server) accelerateList(w http.ResponseWriter, r *http.Request) {
+	if s.Acc == nil {
+		writeJSON(w, http.StatusOK, []any{})
+		return
+	}
+	txs, err := s.Acc.List()
+	if err != nil {
+		writeJSON(w, http.StatusInternalServerError, map[string]any{"error": err.Error()})
+		return
+	}
+	if txs == nil {
+		txs = []store.BoostedTx{}
+	}
+	writeJSON(w, http.StatusOK, txs)
+}