fix: improve api legacy invoke guidance

[hehanlin1996]

Summary

Improve the generic api command error surface for AI-hallucinated / legacy api +invoke --api ... syntax observed in the 2026-05-15 C5 Skill/Agent Runtime evidence (BASE-20260515-002). Instead of Cobra's bare unknown flag: --api plus usage dump, return a structured validation error with the supported raw OpenAPI and schema-driven invocation paths.

Changes

• Detect lark-cli api +invoke --api ... flag parsing failures and convert them to output.ErrWithHint.
• Detect positional lark-cli api +invoke <alias> misuse before dry-run/API execution.
• Suppress the API command usage banner on this validation error so stderr stays machine-readable for agents.
• Add regression tests for both legacy misuse shapes.

Test Plan

• TDD red: go test ./cmd/api -run 'TestApiCmd_LegacyInvoke' -count=1 failed before implementation with unknown flag: --api / no error for +invoke dry-run.
• Unit: go test ./cmd/api -count=1
• Unit: go test ./cmd/... -count=1
• Vet: go vet ./cmd/api
• Related CLI E2E/dry-run regression: go test ./tests/cli_e2e -run 'TestCLIStdinRegression_(SuccessCases|ErrorCases)' -count=1
• Manual dry-run/error surface: go build -buildvcs=false -o /tmp/lark-cli-skill-runtime . && /tmp/lark-cli-skill-runtime api +invoke --api knowledge_base.kpoint_search_v1 --data '{"query":"secboot"}' --dry-run exits 2 and emits structured JSON on stderr.
• Full make unit-test: blocked by a pre-existing unrelated shortcuts/base failure in this environment (TestBaseRecordExecuteReadCreateDelete/upload_attachment_uses_multipart_for_large_file expects .bin as application/octet-stream, but Go/system MIME returns application/x-sega-cd-rom). Reproduced on origin/main at 898e0ee with the same command.

Related Issues

• Related: 能做成一个技能吗 larksuite/cli#897
• Evidence: BASE-20260515-002 (C5-SKILL-DEPLOY)