feat(feishu): migrate Feishu trust config to first-class [feishu] section (Phase 1)

[chaodu-agent]

Summary

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

Current State

• FEISHU_ALLOWED_USERS / FEISHU_ALLOWED_GROUPS env vars in gateway crate
• Double-gating: gateway crate checks AND core checks (can diverge, core side fails open when list empty)
• trusted_bot_ids needed by Receiver for is_bot (Feishu marks bots as sender_type="user")

Target State

[feishu]
allowed_users = ["ou_xxxxxxxxxxxxxxxxxxxx"]
trusted_bot_ids = ["ou_bot1", "ou_bot2"]
# allow_all_users = true  # explicit opt-in only

Tasks

• Add [feishu] section to config schema
• Wire Feishu trust through PlatformTrustConfigs registry
• Migrate FEISHU_ALLOWED_USERS / FEISHU_ALLOWED_GROUPS to core config
• trusted_bot_ids in core config (shared: Receiver reads for is_bot, Handler for admission)
• Eliminate double-gating (gateway = L1 only, trust = core Trust Gate)
• Deprecate gateway env vars (Phase 1 warn → Phase 2 error → Phase 3 remove)
• Update docs and config.toml.example

Notes

• open_id is per-app — same user has different ID in different Feishu apps (document in gotcha)
• Feishu marks other bots as sender_type="user" — unreliable; must match against trusted_bot_ids

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
• LINE equivalent: feat(line): migrate LINE trust config to first-class [line] section (Phase 1) #1355

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