fix(spec-search): use Message objects in run_self_on_task and planner prompt fix

[gazaille4mila]

What does this PR do?

This PR fixes two concrete Spec Search failure modes in diagnose and planner flows.

• Fix 1: run_self_on_task now sends Message objects (not dicts) to teacher_engine.generate.

• Root cause and failing paths:

  • Diagnose tool call site passed OpenAI-style dict messages at src/openjarvis/learning/spec_search/diagnose/tools.py#L281.
  • Cloud engine paths expect Sequence[Message] and dereference message attributes:
    • src/openjarvis/engine/_base.py#L20 (messages_to_dicts) uses m.role.value and m.content.
    • src/openjarvis/engine/cloud.py#L413 (_prepare_anthropic_messages) branches on m.role.value.
    • OpenAI/cloud generation paths call messages_to_dicts, e.g. src/openjarvis/engine/cloud.py#L576.
  • Runtime symptom: dict inputs can raise 'dict' object has no attribute 'role', causing repeated diagnose-tool failures.

• Fix 2: Updated the planner prompt example to a valid numeric hunk (for example @@ -3,1 +3,1 @@), so teacher-produced PATCH edits are parseable and no longer downgraded for malformed diff syntax.

• Root cause and parser path:

  • Planner system prompt example in src/openjarvis/learning/spec_search/plan/planner.py#L48 previously used placeholder hunk header @@ ....
  • Patch application logic in src/openjarvis/learning/spec_search/plan/prompt_diff.py#L50 requires real unified diff hunk headers; parsing starts at src/openjarvis/learning/spec_search/plan/prompt_diff.py#L73.
  • Invalid hunks return None which triggers downgrade warning logic at src/openjarvis/learning/spec_search/plan/prompt_diff.py#L141: "diff could not be applied, downgrading to REPLACE".

How was this tested?

Added a regression test asserting Message(role=Role.USER, ...) is passed and output fields are preserved.

Checklist

• Tests pass (uv run pytest tests/ -v)
  All green except for collecting tests/evals/comparison/test_export_to_table_gen_roundtrip.py failing because of polar import fail (nothing to do with my changes)
• Linter passes (uv run ruff check src/ tests/)
• Formatter passes (uv run ruff format --check src/ tests/)
• New/changed public API has docstrings
  n/a
• Follows registry pattern (if adding new component)
  n/a
• Documentation updated (if applicable)
  n/a