docs(execute_code): document project/strict execution modes (#12073)

Follow-up to PR #11971. Documents the new code_execution.mode config
key and what each mode actually does.

- user-guide/configuration.md: add mode: project to the yaml example,
  explain project vs strict and call out that security invariants are
  identical across modes.
- user-guide/features/code-execution.md: new 'Execution Mode' section
  with a comparison table and usage guidance; update the 'temporary
  directory' note so it reflects that script.py runs in the session
  CWD in project mode (staging dir stays on PYTHONPATH for imports);
  drop stale 'sandboxed' framing from the intro and skill-passthrough
  paragraph.
- getting-started/learning-path.md: update the one-line Code Execution
  summary to match (no longer 'sandboxed environments' — the default
  runs in the session's real working directory).

No code changes.

website/docs/getting-started/learning-path.md

@@ -129,7 +129,7 @@ Not sure what's available? Here's a quick directory of major features:
 | **MCP** | Connect to external tool servers via Model Context Protocol | [MCP](/docs/user-guide/features/mcp) |
 | **Cron** | Schedule recurring agent tasks | [Cron](/docs/user-guide/features/cron) |
 | **Delegation** | Spawn sub-agents for parallel work | [Delegation](/docs/user-guide/features/delegation) |
-| **Code Execution** | Run code in sandboxed environments | [Code Execution](/docs/user-guide/features/code-execution) |
+| **Code Execution** | Run Python scripts that call Hermes tools programmatically | [Code Execution](/docs/user-guide/features/code-execution) |
 | **Browser** | Web browsing and scraping | [Browser](/docs/user-guide/features/browser) |
 | **Hooks** | Event-driven callbacks and middleware | [Hooks](/docs/user-guide/features/hooks) |
 | **Batch Processing** | Process multiple inputs in bulk | [Batch Processing](/docs/user-guide/features/batch-processing) |