* feat(channel): add per-channel proxy_url support for HTTP/SOCKS5 proxies
Allow each channel to optionally specify a `proxy_url` in its config,
enabling users behind restrictive networks to route channel traffic
through HTTP or SOCKS5 proxies. When set, the per-channel proxy takes
precedence over the global `[proxy]` config; when absent, the channel
falls back to the existing runtime proxy behavior.
Adds `proxy_url: Option<String>` to all 12 channel config structs
(Telegram, Discord, Slack, Mattermost, Signal, WhatsApp, Wati,
NextcloudTalk, DingTalk, QQ, Lark, Feishu) and introduces
`build_channel_proxy_client`, `build_channel_proxy_client_with_timeouts`,
and `apply_channel_proxy_to_builder` helpers that normalize proxy URLs
and integrate with the existing client cache.
Closes#3262
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
* fix(channel): add missing proxy_url fields in test initializers
---------
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
Co-authored-by: argenis de la rosa <theonlyhennygod@gmail.com>
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