feat(teams): migrate MS Teams trust config to first-class [teams] section (Phase 1)

[chaodu-agent]

Summary

Migrate MS Teams adapter trust configuration from gateway env vars to a first-class [teams] section in config.toml.

Current State

• Gateway env vars only (GATEWAY_ALLOW_ALL_USERS, GATEWAY_ALLOWED_USERS)
• No per-platform granularity for Teams

Target State

[teams]
allowed_users = ["29:1abc...", "29:2def..."]
trusted_bot_ids = ["28:bot-id"]
# allow_all_users = true  # explicit opt-in only

Tasks

• Add [teams] section to config schema
• Wire Teams trust through PlatformTrustConfigs registry
• is_bot derivation: activity.from.role == "bot" or trusted_bot_ids.contains(activity.from.id)
• Deny-echo via Bot Framework sendToConversation
• Deprecate gateway env vars for Teams
• Update docs and config.toml.example

Notes

• Sender ID format: activity.from.id (e.g., "29:1abc...") — may differ from AAD Object ID
• L1 auth: JWT (OpenID Connect) RS256 verified via Bot Framework OpenID metadata + JWKS
• Verify sender ID format from actual event payloads before finalizing config format

Refs

• Umbrella: umbrella: Phase 1 trust migration — per-platform [section] for all adapters #1356
• ADR: docs(adr): revise identity-trust-none — three-layer architecture #1291

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