feat: per-channel responsePrefix override (#9001)

* feat: per-channel responsePrefix override

Add responsePrefix field to all channel config types and Zod schemas,
enabling per-channel and per-account outbound response prefix overrides.

Resolution cascade (most specific wins):
  L1: channels.<ch>.accounts.<id>.responsePrefix
  L2: channels.<ch>.responsePrefix
  L3: (reserved for channels.defaults)
  L4: messages.responsePrefix (existing global)

Semantics:
  - undefined -> inherit from parent level
  - empty string -> explicitly no prefix (stops cascade)
  - "auto" -> derive [identity.name] from routed agent

Changes:
  - Core logic: resolveResponsePrefix() in identity.ts accepts
    optional channel/accountId and walks the cascade
  - resolveEffectiveMessagesConfig() passes channel context through
  - Types: responsePrefix added to WhatsApp, Telegram, Discord, Slack,
    Signal, iMessage, Google Chat, MS Teams, Feishu, BlueBubbles configs
  - Zod schemas: responsePrefix added for config validation
  - All channel handlers wired: telegram, discord, slack, signal,
    imessage, line, heartbeat runner, route-reply, native commands
  - 23 new tests covering backward compat, channel/account levels,
    full cascade, auto keyword, empty string stops, unknown fallthrough

Fully backward compatible - no existing config is affected.
Fixes #8857

* fix: address CI lint + review feedback

- Replace Record<string, any> with proper typed helpers (no-explicit-any)
- Add curly braces to single-line if returns (eslint curly)
- Fix JSDoc: 'Per-channel' → 'channel/account' on shared config types
- Extract getChannelConfig() helper for type-safe dynamic key access

* fix: finish responsePrefix overrides (#9001) (thanks @mudrii)

* fix: normalize prefix wiring and types (#9001) (thanks @mudrii)

---------

Co-authored-by: Gustavo Madeira Santana <gumadeiras@gmail.com>

CHANGELOG.md

@@ -10,6 +10,7 @@ Docs: https://docs.openclaw.ai
 - Onboarding: add Moonshot (.cn) auth choice and keep the China base URL when preserving defaults. (#7180) Thanks @waynelwz.
 - Docs: clarify tmux send-keys for TUI by splitting text and Enter. (#7737) Thanks @Wangnov.
 - Docs: mirror the landing page revamp for zh-CN (features, quickstart, docs directory, network model, credits). (#8994) Thanks @joshp123.
+- Messages: add per-channel and per-account responsePrefix overrides across channels. (#9001) Thanks @mudrii.
 - Cron: add announce delivery mode for isolated jobs (CLI + Control UI) and delivery mode config.
 - Cron: default isolated jobs to announce delivery; accept ISO 8601 `schedule.at` in tool inputs.
 - Cron: hard-migrate isolated jobs to announce/none delivery; drop legacy post-to-main/payload delivery fields and `atMs` inputs.