Add style and sidecar batch workflows

[cgasgarth]

Goal

Support hero-frame editing followed by reusable batch propagation through darktable-native styles or sidecars, with per-image refinement afterward.

Current state

• The system already supports batched live edits inside a single image session, with stepwise apply/render/verify behavior.
• It does not yet support propagating an edit baseline across multiple selected images.
• There is no agent-facing workflow for creating, applying, or refining darktable styles or sidecar-based baselines.

Scope

• Let the agent package and reapply reusable style or sidecar baselines.
• Support apply-to-selection or batch propagation workflows from a hero image.
• Preserve room for per-image micro-adjustments after propagation.
• Keep the workflow aligned with darktable-native styles/sidecars instead of inventing a separate opaque batch format.

Acceptance Criteria

• A user can edit one frame and ask the agent to propagate that baseline to similar images.
• The workflow uses darktable-native styles or sidecars rather than a custom opaque export format.
• Propagated edits remain editable and refinable on individual images.
• Batch operations have clear safety boundaries, progress reporting, and failure handling.