docs(platforms): assign page owners and establish maintenance guidelines

[chaodu-agent]

Why

The platform schema knowledge base (docs/platforms/schema/*.toml) has 8 platform files with rich capability/feature documentation, but:

1. No assigned owners — when a platform's API changes or our adapter evolves, nobody is specifically responsible for updating the schema
2. No PR checklist — contributors modifying adapter code aren't reminded to update the corresponding schema, so drift accumulates silently
3. Unclear dual-docs relationship — new contributors see both docs/line.md and docs/platforms/schema/line.toml and don't know which to update or why both exist

Without explicit ownership and process, the schema files will become "passing CI but factually stale" documentation — exactly the problem they were created to solve.

Benefits

• Clear accountability — each platform has someone who ensures facts stay current
• Drift prevention at PR time — checklist reminds contributors to update schema when changing adapter behavior
• Zero onboarding confusion — new maintainers immediately understand: TOML = machine facts, Markdown = human setup guide
• Sustainable long-term — without this, 2800 lines of TOML will silently rot within 6 months

Proposed Actions

1. Assign platform page owners

Platform	Owner
line	TBD
slack	TBD
telegram	TBD
discord	TBD
feishu	TBD
wecom	TBD
googlechat	TBD
teams	TBD

2. Add to PR template / checklist

When the PR touches crates/openab-gateway/src/adapters/*.rs:

• Updated docs/platforms/schema/<platform>.toml if feature status or capabilities changed

3. Document dual-docs architecture in README

Already partially done in #1295 (architecture diagram + "How to update" section). Verify the explanation is clear and complete.

Context

Identified during group review of #1295. Per #1294: "Each per-platform page is owned by that platform's maintainer."

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