Add OpenStock agent CLI skill

skills/openstock-agent-cli/references/commands/api/call/guide.md

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+# `openstock api call`
+
+Purpose: directly call a KIS GET endpoint with access-token headers.
+
+Usage:
+
+```bash
+openstock api call /uapi/... --param tr_id=... --param KEY=VALUE
+```
+
+Inputs: `endpoint`, repeated `--param KEY=VALUE`.
+
+Reads: KIS credentials and access token from config/env.
+
+External IO: KIS endpoint GET.
+
+Output fields: `broker`, `endpoint`, `params`, `request_semantics`, `response`, `response_semantics`.
+
+Agent rule: prefer typed commands; use this only for endpoints not yet implemented as stable commands.