add fee-aware mining, coinbase validation, and reorg-safe orphan handling

Mining: blocks now include mempool txs, select spendable txs by fee, and pay coinbase as base reward + fees in main.c.
 - Consensus: block validation now enforces coinbase accounting and rejects invalid coinbase placement, including coinbase on amount2, in block.c and transaction.c.
 - Chain state: rollback now rebuilds currentSupply/currentReward, and block addition preflights spendability before mutating balances in chain.c.
 - Orphans/reorgs: orphan retry is safer, rollback-triggered sync reattaches orphans immediately, and transient orphan failures no longer drop blocks in orphan_pool.c and main.c.
 - Networking/mempool: node lifecycle now initializes the mempool, broadcasts can exclude one peer, and mempool snapshotting supports mining selection in net_node.c and txmempool.c.
 - Ledger simulation: added non-mutating spendable-transaction selection for block assembly in balance_sheet.c.

src/nets/orphan_pool.c

@@ -197,13 +197,8 @@ size_t OrphanPool_AttemptAttach(blockchain_t* chain) {
                     i = (size_t)-1; // reset outer loop
                     break;
                 } else {
-                    // Chain_AddBlock rejected it (maybe invalid). Drop it.
-                    Block_Destroy(e->block);
-                    DynArr_remove(g_orphans, i);
-                    n = DynArr_size(g_orphans);
-                    i = (size_t)-1;
-                    madeProgress = true;
-                    break;
+                    // Keep the orphan around; rejection may be temporary while the local tip is being reorged.
+                    continue;
                 }
             }
         }