feat(engine): add workflow.dir, workflow.file, workflow.name template variables

[PolyphonyRequiem]

Summary

Adds three new template variables available in all agent contexts:

• {{ workflow.dir }} — absolute path to the workflow YAML's parent directory
• {{ workflow.file }} — absolute path to the workflow YAML file itself
• {{ workflow.name }} — workflow name from the YAML config

Motivation

Script agents specify script paths in args, but these resolve relative to CWD (where conductor run is invoked). When workflows live in a registry (e.g., ~/.conductor/registries/twig/), co-located scripts can't be found because CWD is the user's project directory, not the registry.

{{ workflow.dir }} solves this by letting scripts build paths relative to the workflow file:

agents:
  - name: detector
    type: script
    command: pwsh
    args:
      - "-File"
      - "{{ workflow.dir }}/scripts/detect-state.ps1"

This matches how !file tags already resolve prompt file paths relative to the workflow file.

Changes

• src/conductor/engine/context.py: Add workflow_dir, workflow_file, workflow_name fields to WorkflowContext. Include them in build_for_agent() output under the workflow dict (all context modes).
• src/conductor/engine/workflow.py: Set the new fields from workflow_path during WorkflowEngine.__init__().
• tests/test_engine/test_context.py: Tests for metadata in accumulate/explicit modes, and empty-string omission.

Design decisions

• Available in all context modes — workflow metadata is lightweight (3 strings) and fundamental. Unlike agent outputs, these shouldn't be filtered by explicit mode.
• Empty strings omitted — when workflow_path is None (e.g., tests), the fields are empty strings and excluded from the context dict to avoid polluting templates.
• No breaking changes — existing workflow.input behavior is unchanged. New fields are additive.

Testing

• 139 context + workflow engine tests pass
• New tests cover accumulate mode, explicit mode, and empty-metadata omission

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
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Additional details and impacted files

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