feat: vote-hash supermajority engine with skip-path solver

[7layermagik]

Summary

• Vote-hash supermajority engine — accumulates vote-transaction stake per bankhash per slot, detects 2/3+1 confirmation with early-exit and timeout semantics
• Skip-path solver — BFS solver that finds a valid sequence of block/skip decisions chaining from a parent bankhash to the vote-confirmed target hash, with hash-dedup to prevent state explosion
• Consensus coordinator — bridges the supermajority engine and skip-path solver; queries confirmed hashes, runs the solver, returns per-slot UseBlock decisions
• Replay integration — wires the coordinator into the replay loop with bankhash mismatch detection, chain verification, enriched diagnostic artifacts (written to per-run log directory), and configurable halt/warn policy
• Epoch boundary handling — snapshots epoch data at SubmitBlock time for consistent stake views, refreshes authorized voters cache at epoch transitions

Key design decisions

• Post-execution confirmation only (solver requires bankhashes which are post-execution, so pre-execution path selection is not possible)
• VoteConfirmationTimeoutSlots = 32 — slots without supermajority after timeout yield NoSupermajority
• Early confirmation: if supermajority is reached before timeout, returns immediately without waiting
• Fail-closed: missing authorized voters returns NeedWait, not silent skip

Commits

1. 35d6fb1 — Core engine: supermajority accumulator, skip-path solver, consensus coordinator
2. e349ddf — Replay integration: wiring, diagnostic artifacts, config, epoch boundary handling
3. fe9fdea — Test coverage: 25 tests across all components

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