feat: add chat-members-add shortcut

[zhangheng023]

Summary

Adds a new im +chat-members-add shortcut that adds users and/or bots to an existing group chat. It replaces the raw im chat.members create meta API call — which requires two separate JSON blobs (--params for chat_id/member_id_type/succeed_type, --data for id_list) and an implicit rule that a user ID's format must match member_id_type while bot IDs are always app_id — with two plain flags (--users, --bots) and a fixed member_id_type=open_id, removing that footgun entirely.

Changes

• New shortcut shortcuts/im/im_chat_members_add.go: --chat-id (required), --users (comma-separated ou_xxx, max 50), --bots (comma-separated cli_xxx, max 5), --succeed-type (0 = strict / 1 = partial-success, default 1)
• Partial-failure reporting via an ok:false ledger envelope (mirrors the existing +feed-shortcut-create convention), covering all three server response buckets (invalid_id_list, not_existed_id_list, pending_approval_id_list) so a member that failed to join is never miscounted as succeeded
• Registered in shortcuts/im/shortcuts.go
• New skill reference doc skills/lark-im/references/lark-im-chat-members-add.md; SKILL.md Shortcuts/permission tables updated
• Two existing docs (lark-im-chat-create.md, affordance/im.md) updated to point their two-step invite examples at the new shortcut instead of the raw meta command
• Incidental fix: an unrelated, pre-existing doc-drift bug on +messages-search (its affordance example still pinned --as user after a recent PR made it dual-identity) was also corrected, since it was blocking a clean go test signal for this branch

Test Plan

• Unit tests pass (go test ./shortcuts/im/..., go test ./internal/affordance/...) — covers flag validation, dry-run, the full ledger (all-success / partial-failure across all three failure buckets), and the --succeed-type strict/partial modes
• Build and static checks pass
• Manual verification: lark-cli im +chat-members-add --chat-id oc_xxx --users ou_xxx --bots cli_xxx against a real Feishu tenant — confirmed the partial-failure ledger output and the empty --users/--bots validation error

Related Issues

• None