wrap: chain verify + manifest verify + LICENSE + final docs

- internal/chain: end-to-end chain verification. Walks head → genesis,
  verifies every cert (Ed25519 or STM as appropriate), and checks
  continuity at every boundary:
    epoch:    same or +1 from previous
    hash:     current.previous_hash == previous.hash
    AVK:      same epoch  → equal aggregate_verification_key
              new epoch   → matches previous.protocol_message.next_aggregate_verification_key
- cmd: 'verify chain' subcommand + 'verify manifest <dir>' for SHA-checking
  downloaded immutable files
- internal/manifest: per-file SHA-256 verification against the digests.json
  shipped in the snapshot's digests archive
- MCP: 8th tool 'mithril_verify_chain' for agent-driven full-chain verify
- README: complete rewrite — status table, architecture, gotchas, MCP
  tool surface, exit code contract, build instructions
- LICENSE: Apache-2.0 (matches upstream Mithril)

Verified end to end against live networks:
  preprod  chain  90 certs (89 STM + 1 genesis)  1124 wins   ✓
  mainnet  chain  89 certs (88 STM + 1 genesis)  210921 wins ✓

That's the wrap. Pure-Go consensus-correct Mithril client, single 10 MB
static binary, MCP-native, no CGo, no upstream Rust runtime.

go.sum

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