feat(codex): redeem banked usage-limit resets via /usage reset (#64280)

OpenAI lets ChatGPT-plan Codex users bank rate-limit reset credits, but
until now they could only be redeemed from the Codex CLI/app or the
website. This wires the same backend API into Hermes:

- /usage on the openai-codex provider now shows "You have N resets
  banked - use /usage reset to activate" (parsed from the
  rate_limit_reset_credits field the /usage endpoint already returns).
- New /usage reset subcommand (CLI + gateway) redeems one banked
  credit via POST .../rate-limit-reset-credits/consume with a UUID
  idempotency key, mirroring codex-rs backend-client semantics
  (PathStyle /wham vs /api/codex, ChatGPT-Account-Id header,
  reset/nothing_to_reset/no_credit/already_redeemed outcomes).
- Guard: redemption is refused while no rate-limit window is fully
  exhausted, since a banked reset restores the FULL 5h + weekly
  allowance and spending it early wastes it. /usage reset --force
  overrides. Zero banked credits and non-codex providers are refused
  with clear messages; nothing_to_reset reports the credit was NOT
  spent.
- i18n: new gateway.usage.unknown_subcommand / reset_wrong_provider
  keys across all 16 locales; docs updated (cli.md, messaging index).

Tested with unit tests plus a real-socket E2E against a local fake
Codex backend exercising redeem/guard/force and the /usage hint.

website/docs/user-guide/cli.md

@@ -90,6 +90,8 @@ The bar adapts to terminal width — full layout at ≥ 76 columns, compact at 5
 
 Use `/usage` for a detailed breakdown including per-category costs (input vs output tokens).
 
+On the `openai-codex` provider, `/usage` also shows any banked usage-limit resets on your ChatGPT account ("You have N resets banked - use /usage reset to activate"). `/usage reset` redeems one banked reset, fully restoring your 5-hour and weekly limits. Hermes refuses to redeem while your limits aren't exhausted (a banked reset restores the full allowance, so spending it early wastes it) — pass `/usage reset --force` to redeem anyway.
+
 ### Session Resume Display
 
 When resuming a previous session (`hermes -c` or `hermes --resume <id>`), a "Previous Conversation" panel appears between the banner and the input prompt, showing a compact recap of the conversation history. See [Sessions — Conversation Recap on Resume](sessions.md#conversation-recap-on-resume) for details and configuration.

website/docs/user-guide/messaging/index.md

@@ -172,7 +172,7 @@ hermes gateway status --system         # Linux only: inspect the system service
 | `/compress` | Manually compress conversation context |
 | `/title [name]` | Set or show the session title |
 | `/resume [name]` | Resume a previously named session |
-| `/usage` | Show token usage for this session |
+| `/usage` | Show token usage for this session (`/usage reset [--force]` redeems a banked Codex limit reset) |
 | `/insights [days]` | Show usage insights and analytics |
 | `/reasoning [level\|show\|hide]` | Change reasoning effort or toggle reasoning display |
 | `/voice [on\|off\|tts\|join\|leave\|status]` | Control messaging voice replies and Discord voice-channel behavior |