Convert the salvaged text-debounce delays from HERMES_* env vars to
config.yaml (gateway.platforms.<name>.extra.text_batch_delay_seconds /
text_batch_split_delay_seconds), per the '.env is for secrets only'
policy. Adds a finite/non-negative guard so bad YAML values fall back to
the defaults instead of crashing asyncio.sleep().
- whatsapp.py / weixin.py: read delays via _coerce_float_extra(config.extra)
- update Weixin content-dedup regression test for the deferred dispatch path
- add text-debounce coverage (whatsapp + weixin): defaults, config override,
bad-value fallback, env-var-ignored, burst-collapse, lone-message
- docs: WhatsApp + Weixin config keys
cddb7283d9