Auto-wrap missing Jinja expressions and require non-empty action_id for action nodes

[zhongkaifu]

Motivation

• Avoid Jinja parse/runtime errors caused by param strings that look like Jinja variable access but are missing {{ }} wrapping.
• Reduce false positives by performing a compile-time check before auto-wrapping suspected expressions.
• Ensure workflow correctness by enforcing that nodes of type action always provide a non-empty action_id so they can be executed.

Description

• Added POTENTIAL_JINJA_EXPR, looks_like_missing_jinja and has_unwrapped_variable helpers to velvetflow/jinja_utils.py, where has_unwrapped_variable now uses get_jinja_env().compile_expression to verify candidates.
• Updated velvetflow/verification/jinja_validation.py to use has_unwrapped_variable in _normalize_jinja_expr so unwrapped but valid expressions are auto-wrapped as {{ ... }}.
• Added a validation rule in velvetflow/verification/node_rules.py that emits a MISSING_REQUIRED_PARAM ValidationError for action nodes missing or having an empty action_id, with messaging that directs the error context to be analyzed/handled by an LLM and repair tools.

Testing

• No automated tests were executed for these changes.
• Changes were committed locally and prepared for PR, but the test suite and CI were not run as part of this rollout.

---

Codex Task