fix(genesis): use a deterministic configured timestamp

[shu-unifra]

The genesis generator currently writes vm.unixTime() / 1000 into the block header. Running it in a different second changes the genesis hash even when all deployment inputs are identical.

Read a fixed Unix timestamp from genesis.TIMESTAMP instead. The template uses 0, and older configs without the field also default to 0. Explicit timestamps are accepted up to uint64::MAX; negative, malformed, and overflowing inputs fail. Keep deployment salt, other configuration, and build versions fixed when reproducing a genesis.

Changing from a previously generated timestamp changes the genesis hash. Regenerate the Reth mainnet genesis JSON, DOGEOS_MAINNET_GENESIS_HASH and its test, the rollup-node chain spec, and matching release images/tag together with the other pending mainnet genesis fixes. This change does not update an initialized network.

Validation:

• forge test --evm-version cancun: 560 passed, 0 failed, including timestamp defaults, explicit zero/nonzero values, the uint64 boundary, invalid inputs, and JSON serialization.
• python3 scripts/integration/test-eip2935.py --genesis-only: checks an explicit nonzero timestamp through the real gen-configs.sh entrypoint, then repeats generation in a later wall-clock second and compares the entire genesis YAML byte-for-byte. This check already runs in CI.
• RPC smoke-check regression tests: 5 passed.
• Prettier and git diff --check: passed.