[Bug] `start-devnet.sh` generates 4 nodes but only 3 validators in genesis

## Summary

`./scripts/start-devnet.sh` creates 4 node directories (`node0`-`node3`) but the generated `genesis.json` only contains 3 validators (`validator-0` through `validator-2`). `node3` runs as a non-validator participant with no representation in the genesis validator set.

## Evidence

**Genesis validator set** (`devnet/genesis.json`):
- `validator-0` — `0xf39f...2266`
- `validator-1` — `0x7099...79c8`
- `validator-2` — `0x3c44...93bc`

**Node directories created**: `node0/`, `node1/`, `node2/`, `node3/`

**`node3/config/node.json`** references `validator-3` with its own `validator_id` (`19edeb6d...`), BLS/Ed25519 keys, and unique ports (9030-9035, RPC 8575-8576). However, this validator is absent from `genesis.json` — both from the `cipherbft.validators[]` array and from `alloc` (no pre-funded account).

## Impact

- `node3` cannot participate in consensus (not in the validator set).
- With only 3 validators (`n=3, f=0`), the network has **zero fault tolerance** — any single node failure halts consensus.
- `node3`'s peer list includes all 3 genesis validators, and `node0`'s peer list excludes `node3`, confirming the asymmetry is baked into the config generation.

## Expected Behavior

If `start-devnet.sh` is intended to produce a 4-validator devnet:
1. `genesis.json` should include `validator-3` in `cipherbft.validators[]`.
2. `alloc` should include `validator-3`'s address with a funded balance.
3. All node configs should list the other 3 nodes as peers (node0-node2 currently only list 2 peers each, missing node3).

## Likely Root Cause

The script creates `N` node directories but the genesis generation logic uses a hardcoded or off-by-one validator count (`N-1` instead of `N`). Alternatively, `node3` may be intentionally a non-validator full node, in which case the `key_name: "validator-3"` naming is misleading.

## Steps to Reproduce

```bash
./scripts/start-devnet.sh
cat devnet/genesis.json | jq '.cipherbft.validators | length'
# Returns: 3
ls -d devnet/node*/
# Returns: node0/ node1/ node2/ node3/
```