feat: migrate-from-smush + Picture-tag rewriter (v0.2.0)

Unblocks production use on sites previously running Smush.

migrate-from-smush:
  - Reads wp-smpro-smush-data postmeta, writes _h4b_img_optim marker
  - --dry-run / --force-rescan / --remove-smush-meta / --limit flags
  - Verified: 100 attachments migrated cleanly on dev.rds.ink,
    bulk count drops from 734 → 634

Picture_Tag rewriter:
  - Hooks the_content + post_thumbnail_html + widget_text + Elementor
    frontend + wp_get_attachment_image at priority 99
  - Wraps <img> in <picture><source avif><source webp><img></picture>
    when sibling files exist
  - Double-wrap protection via byte-range tracking of existing <picture> blocks
  - Per-image opt-out via data-no-h4b attribute
  - Cached sibling lookups per request
  - 8 edge-case tests pass

LOC: 2480 (was 1997). Adds class-cli-migrate.php (193 LOC) and
class-picture-tag.php (284 LOC).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

CHANGELOG.md

@@ -5,6 +5,38 @@ All notable changes to **h4b-image-optim** will be documented here.
 Format follows [Keep a Changelog](https://keepachangelog.com/en/1.1.0/) and
 [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [0.2.0] — 2026-05-19
+
+Added migrate-from-smush + Picture-tag rewriter. The plugin is now usable
+end-to-end on a site that previously ran Smush — no double-processing, and
+WebP / AVIF actually get served to visitors.
+
+### Added
+- **`wp h4b-img migrate-from-smush`** — reads Smush's `wp-smpro-smush-data`
+  postmeta, writes equivalent `_h4b_img_optim` markers so our bulk command
+  skips already-optimised attachments.
+  - `--dry-run` to see counts only
+  - `--force-rescan` to mark for re-optimisation instead (use when migrating
+    off Smush completely)
+  - `--remove-smush-meta` to delete the Smush postmeta after migration
+- **`Picture_Tag`** rewriter (the_content + post_thumbnail_html + widget_text +
+  Elementor frontend + wp_get_attachment_image filters at priority 99). Wraps
+  `<img>` tags with `<picture><source type="image/avif"><source type="image/webp"><img></picture>`
+  when sibling files exist on disk.
+  - Skips images already inside a `<picture>` block (double-wrap protection
+    via byte-range tracking)
+  - Skips images with `data-no-h4b` attribute (per-image opt-out)
+  - Resolves siblings either alongside the JPG (`foo.jpg.webp`) or in Smush's
+    `wp-content/smush-webp/` mirror tree
+  - Caches sibling lookups per request to keep it cheap
+  - Preserves srcset, sizes, alt, class, and all other original `<img>` attrs
+
+### Verified
+- migrate-from-smush: 100 attachments migrated cleanly on dev.rds.ink
+- bulk count correctly drops after migration (734 → 634)
+- Picture_Tag: 8 edge-case tests pass (no siblings, multiple images, opt-out,
+  srcset preservation, external URLs, no `<img>`, existing `<picture>`, mixed)
+
 ## [0.1.0] — 2026-05-19
 
 Initial MVP. Replaces Smush Pro's optimisation pipeline without the