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/store/accelerator.go

@@ -0,0 +1,79 @@
+package store
+
+// BoostedTx represents a transaction whose priority has been adjusted
+// via bitcoind's prioritisetransaction RPC.
+type BoostedTx struct {
+	Txid            string  `json:"txid"`
+	OriginalFeerate float64 `json:"original_feerate"` // sat/vB before boost
+	BoostedFeerate  float64 `json:"boosted_feerate"`  // sat/vB after boost
+	FeeDelta        int64   `json:"fee_delta"`        // sats applied
+	Vsize           int64   `json:"vsize"`
+	BoostedAt       int64   `json:"boosted_at"` // unix timestamp
+}
+
+const acceleratorSchema = `
+CREATE TABLE IF NOT EXISTS boosted_txs (
+    txid              TEXT PRIMARY KEY,
+    original_feerate  REAL NOT NULL,
+    boosted_feerate   REAL NOT NULL,
+    fee_delta         INTEGER NOT NULL,
+    vsize             INTEGER NOT NULL,
+    boosted_at        INTEGER NOT NULL
+);
+`
+
+// migrateAccelerator ensures the boosted_txs table exists.
+func (s *BlockStore) migrateAccelerator() error {
+	_, err := s.db.Exec(acceleratorSchema)
+	return err
+}
+
+// InsertBoostedTx records a newly boosted transaction.
+func (s *BlockStore) InsertBoostedTx(tx BoostedTx) error {
+	_, err := s.db.Exec(
+		`INSERT OR REPLACE INTO boosted_txs(txid, original_feerate, boosted_feerate, fee_delta, vsize, boosted_at)
+		 VALUES (?, ?, ?, ?, ?, ?)`,
+		tx.Txid, tx.OriginalFeerate, tx.BoostedFeerate, tx.FeeDelta, tx.Vsize, tx.BoostedAt,
+	)
+	return err
+}
+
+// RemoveBoostedTx deletes a boosted tx record (confirmed, dropped, or cancelled).
+func (s *BlockStore) RemoveBoostedTx(txid string) error {
+	_, err := s.db.Exec(`DELETE FROM boosted_txs WHERE txid = ?`, txid)
+	return err
+}
+
+// ListBoostedTxs returns all currently boosted transactions, newest first.
+func (s *BlockStore) ListBoostedTxs() ([]BoostedTx, error) {
+	rows, err := s.db.Query(
+		`SELECT txid, original_feerate, boosted_feerate, fee_delta, vsize, boosted_at
+		 FROM boosted_txs ORDER BY boosted_at DESC`,
+	)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	var out []BoostedTx
+	for rows.Next() {
+		var tx BoostedTx
+		if err := rows.Scan(&tx.Txid, &tx.OriginalFeerate, &tx.BoostedFeerate, &tx.FeeDelta, &tx.Vsize, &tx.BoostedAt); err != nil {
+			return nil, err
+		}
+		out = append(out, tx)
+	}
+	return out, rows.Err()
+}
+
+// GetBoostedTx returns a single boosted tx by txid, or nil if not found.
+func (s *BlockStore) GetBoostedTx(txid string) (*BoostedTx, error) {
+	var tx BoostedTx
+	err := s.db.QueryRow(
+		`SELECT txid, original_feerate, boosted_feerate, fee_delta, vsize, boosted_at
+		 FROM boosted_txs WHERE txid = ?`, txid,
+	).Scan(&tx.Txid, &tx.OriginalFeerate, &tx.BoostedFeerate, &tx.FeeDelta, &tx.Vsize, &tx.BoostedAt)
+	if err != nil {
+		return nil, err
+	}
+	return &tx, nil
+}