feat(teams): full [teams] section — credentials + connection config-first

[chaodu-agent]

Summary

Extend [teams] beyond the trust fields (#1366): graduate from shared PlatformTrustConfig to a dedicated struct. Config-first invariant: [teams] → TEAMS_* env → default.

Fields to add

app_id, app_secret, allowed_tenants, webhook_path, oauth_endpoint, openid_metadata (env fallbacks: TEAMS_*)

Tasks

• Dedicated TeamsConfig (core-side) + resolve; keep existing trust fields
• Bridge + AppState::apply_teams_config()
• docs (msteams-selfhosted.md / msteams-enterprise.md) + config-reference.md
• Regression: env-only unchanged

Refs

Umbrella: #1375 · Trust slice: #1366 · Reference: TelegramConfig (#1297)

[github-actions]

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