fix(docker): seed gateway_state.json from HERMES_GATEWAY_BOOTSTRAP_STATE on first boot (#37896)

On a fresh volume there is no gateway_state.json, so the boot reconciler
(cont-init.d/02-reconcile-profiles) registers the gateway-default s6 slot
but leaves it down — it only auto-starts when the last recorded state was
"running". A freshly-provisioned container therefore comes up with the
gateway down until something starts it (e.g. the dashboard's start button).

Add a generic, first-boot-only env-seed in stage2-hook.sh (which runs
before 02-reconcile-profiles): when HERMES_GATEWAY_BOOTSTRAP_STATE=running
and no gateway_state.json exists yet, seed {"gateway_state":"running"} so
the reconciler brings the supervised slot up on the very first boot.

This mirrors the existing HERMES_AUTH_JSON_BOOTSTRAP pattern: it seeds the
same state file the reconciler already consults, guarded by [ ! -f ] so
persisted runtime state always wins on later boots (a deliberately-stopped
gateway stays stopped across restarts). Only the literal "running" is
honoured (the sole value in the reconciler's _AUTOSTART_STATES).

Generic container contract — no host-specific code. Useful to any
orchestrator that provisions a blank volume and wants the gateway up from
first boot (the supervised gateway/dashboard already work on such hosts;
only the first-boot autostart was missing because the CLI lifecycle
commands can't drive the s6 layer when container self-detection misses).

Adds a shell-level contract test and documents the env var.

website/docs/reference/environment-variables.md

@@ -519,6 +519,7 @@ Advanced per-platform knobs for throttling the outbound message batcher. Most us
 | `HERMES_GATEWAY_BUSY_INPUT_MODE` | Default gateway busy-input behavior: `queue`, `steer`, or `interrupt`. Can be overridden per chat with `/busy`. |
 | `HERMES_GATEWAY_BUSY_ACK_ENABLED` | Whether the gateway sends an acknowledgment message (⚡/⏳/⏩) when a user sends input while the agent is busy (default: `true`). Set to `false` to suppress these messages entirely — the input is still queued/steered/interrupts as normal, only the chat reply is silenced. Bridged from `display.busy_ack_enabled` in `config.yaml`. |
 | `HERMES_GATEWAY_NO_SUPERVISE` | Inside the s6-overlay Docker image, opt out of auto-supervision when running `hermes gateway run` and use pre-s6 foreground semantics (no auto-restart, gateway is the container's main process). Truthy values: `1`, `true`, `yes`. Equivalent to the `--no-supervise` CLI flag. No-op outside the s6 image. |
+| `HERMES_GATEWAY_BOOTSTRAP_STATE` | Inside the s6-overlay Docker image, declare the gateway's **initial** supervised state on a fresh volume. On a blank volume there is no persisted `gateway_state.json`, so the boot reconciler registers the `gateway-default` slot but leaves it **down** (it only auto-starts when the last recorded state was `running`). Set this to `running` and the first-boot setup hook seeds `gateway_state.json` *before* the reconciler runs, so the gateway comes up on the very first boot. Only the literal value `running` is honoured. First-boot-only: an existing `gateway_state.json` is never overwritten, so a deliberately-stopped gateway stays stopped across restarts. No-op outside the s6 image. |
 | `HERMES_FILE_MUTATION_VERIFIER` | Enable the per-turn file-mutation verifier footer (default: `true`). When enabled, Hermes appends an advisory listing any `write_file` / `patch` calls that failed during the turn and were not superseded by a successful write. Set to `0`, `false`, `no`, or `off` to suppress. Mirrors `display.file_mutation_verifier` in `config.yaml`; the env var wins when set. |
 | `HERMES_CRON_TIMEOUT` | Inactivity timeout for cron job agent runs in seconds (default: `600`). The agent can run indefinitely while actively calling tools or receiving stream tokens — this only triggers when idle. Set to `0` for unlimited. |
 | `HERMES_CRON_SCRIPT_TIMEOUT` | Timeout for pre-run scripts attached to cron jobs in seconds (default: `120`). Override for scripts that need longer execution (e.g., randomized delays for anti-bot timing). Also configurable via `cron.script_timeout_seconds` in `config.yaml`. |