fix(core): normalize content-only MCP tool results

[JJasonSun]

Summary

• preserve the raw MCP tool-result envelope while exposing an existing structuredContent or structured_content object through the canonical structuredContent field
• parse a JSON object from a text content block when a content-only result omits structured content
• leave prose, invalid JSON, arrays, scalar JSON, Markdown fences, and combined fragments unchanged
• apply the normalized result to direct MCP calls and the plan_call / run_call / get_call_run CLI workflow
• document the raw MCP envelope, SDK field names, workflow handoff fields, and stable CLI result paths

Testing

• pnpm test
• pnpm check
• pnpm pack:dry-run
• git diff --check

Release

Adds patch changesets for @call-e/core and @call-e/cli.

Relates to CALLE-AI/awesome-phone-call-agents#158