dgb: wire faithful #82 reconstruct closure into the run-loop (replace nullopt stub)

[frstrtr]

What

main_dgb.cpp --run now binds tracker().m_on_block_found to the FAITHFUL make_reconstruct_closure_from_template (#280) in place of the interim return nullopt stub. Three version-agnostic won-block inputs, bound to the LIVE sharechain tracker:

• won_share_fields_fn -> share.m_min_header + m_merkle_link (dgb: won_share_inputs seam — share-side half of #82 faithful reconstruct closure #279, verbatim)
• gentx_bytes_fn -> generate_share_transaction(...).GentxCoinbase.bytes (dgb(#82): expose SSOT gentx bytes for won-block reconstruction #173 SSOT); v36_active re-derived from the share compile-time version inside GST (share_check.hpp:943), byte-identical to the verify-path invocation (share_check.hpp:1728)
• template_other_txs_fn -> captured-GBT non-coinbase set (dgb(#82): reconstruct won block from captured GBT template, not share refs #271); EMPTY today (no per-job template retention + unfed embedded mempool => coinbase-only block), correct-and-empty, NOT fail-closed

Threading / safety

Fires on the COMPUTE thread already holding the tracker lock (attempt_verify -> m_on_block_found, share_tracker.hpp:537), so the fns read tracker().chain DIRECTLY and do NOT take read_tracker() (would self-deadlock — corrected consume-seam audit). Fail-closed end to end: any builder error -> nullopt (announce + audit; the RPC submitblock fallback still fires independently).

Scope / fence

• Single file: src/c2pool/main_dgb.cpp. No consensus / share-format / PPLNS surface; p2pool-merged-v36 surface NONE.
• Build EXIT=0; selftest OK.
• HOLD merge — BLOCK-REWARD-CRITICAL surface-for-tap. dgb: v36 donation version-gate (pillar 4 of modern-layer activation) #82 stays OPEN pending a live UpdateTip won-block test (won-block-reaches-network).