nmc(PB): name-operation relay path + fee flow into template

[frstrtr]

NMC P1 PB — name-operation relay path + fee flow

§4 review CLEARED (integrator, all 3 open items accepted). Cuts NMC PB.

Adds the one NMC tx-class with no BTC/DOGE analog: the Namecoin name operations (name_new / name_firstupdate / name_update). c2pool is a merge-miner, not a name registry, so name txs are relayed into the block template WITHOUT name-db consensus validation — SPV-trust in the configured namecoind backend; namecoind owns name-db consensus.

Changes (src/impl/nmc/ only — per-coin isolation, btc tree read-only)

• coin/mempool.hpp
  • classify_name_op() — version-marker (getNamecoinVersion() == 0x7100) and a leading name opcode (OP_1/OP_2/OP_3) on an output script. The version gate is the false-positive guard: a bare OP_1..OP_3 output in a plain Bitcoin-version tx (taproot / segwit-v1 / bare multisig) is not classified as a name op.
  • MempoolEntry carries NameOp + TxSource provenance (Daemon-trusted vs PeerRelay) — the SPV-trust boundary. name_op_count() / trusted_name_op_count() queries.
  • Name-tx fees flow through the existing get_sorted_txs_with_fees → coinbasevalue path unchanged — name ops are NOT special-cased in payout (Bitcoin subsidy schedule).
• test/nmc_mempool_name_test.cpp — 9 KATs: classify (incl. false-positive guard + wrong-version + name-version-without-name-script), admission + provenance tagging, and a name-tx fee reaching the template coinbasevalue (subsidy(2) + 7000).
• test/CMakeLists.txt + build.yml — nmc_mempool_name_test registered in CMake and both allowlist lines (avoids a dgb: conform subsidy to p2pool-dgb-scrypt oracle (COIN=1e6, weeks+1) [COMPAT] #137 NOT_BUILT sentinel).

Local verification

• nmc_mempool_name_test — 9/9 PASS
• nmc_template_builder_test (existing mempool consumer, after the mempool.hpp edits) — 17/17 PASS, no regression

Deferred to PF (per §4 — caveats, not PB blockers)

1. Bind name-op trust to the daemon source (PeerRelay name txs admitted but not trusted).
2. v36 short-circuit (if constexpr ShareT::version < 36 return {}) so NMC merged work can't mint on a pre-v36 BTC share.
3. Assert no aux-slot collision across the registered vector<AuxChain> at actual tree size.