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>

h4b-image-optim.php

@@ -3,7 +3,7 @@
  * Plugin Name:       H4B Image Optim
  * Plugin URI:        https://gitea.help4bis.com/help4bis/h4b-image-optim
  * Description:       ICC-safe image optimisation with WebP + AVIF generation. Replaces Smush Pro without the grey-wash bug. No CDN.
- * Version:           0.1.0
+ * Version:           0.2.0
  * Author:            help4bis (Henk + Claude)
  * Author URI:        https://help4bis.com
  * License:           GPL-2.0-or-later
@@ -17,7 +17,7 @@ if ( ! defined( 'ABSPATH' ) ) {
 	exit;
 }
 
-define( 'H4B_IMG_OPTIM_VERSION', '0.1.0' );
+define( 'H4B_IMG_OPTIM_VERSION', '0.2.0' );
 define( 'H4B_IMG_OPTIM_FILE', __FILE__ );
 define( 'H4B_IMG_OPTIM_DIR', plugin_dir_path( __FILE__ ) );
 define( 'H4B_IMG_OPTIM_URL', plugin_dir_url( __FILE__ ) );