feat: add Writing Model, Image Model, and Cost columns to posts list

v0.4.1 — Three new columns on the WordPress Posts admin page showing
which LLM wrote each article, which model generated its featured image,
and the total API cost. Model names shortened for compact display with
full ID in tooltip. Cost queries the generation_log table, skipping
the DB hit entirely for non-generated posts.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

CHANGELOG.md

@@ -5,6 +5,17 @@ All notable changes to PRAutoBlogger will be documented in this file.
 Format follows [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project uses [Semantic Versioning](https://semver.org/).
 
+## [0.4.1] — 2026-04-19
+
+### Added
+- **Posts list columns: Writing Model, Image Model, Cost.** Three new columns
+  on the WordPress Posts admin page. Writing Model shows the LLM that wrote the
+  article, Image Model shows the model that generated the featured image, and
+  Cost shows the total API spend for generating that article (summed from the
+  generation log). All columns show "—" for non-generated posts. Writing Model
+  is sortable. Model names are shortened (provider prefix stripped) with full
+  ID in a tooltip.
+
 ## [0.4.0] — 2026-04-19
 
 ### Added