feat: deterministic image composer — OG + square variants, branding, baked caption (v0.17.0)

Commit 2 (final scope) of the in-plugin editorial image pipeline
(ARCHITECTURE.md #21). A deterministic local composer now runs between
provider bytes and sideload: Image A yields a corner-marked featured
(1200x632) + branded OG (1200x630, teal band, logo, baked caption in
Poppins SemiBold) + square card (1080x1080, cream panel, Poppins Bold,
teal footer with the reverse lockup); Image B gets the corner mark only.

- Capability ladder: imagick (full compositing) -> wp_get_image_editor
  resize-only (unbranded, WARNING once) -> pass-through (WARNING once);
  probe cached in prautoblogger_image_compose_capability, fingerprinted
  by PHP version + imagick/gd presence so host flips auto-invalidate.
  compose() never throws; composition can never fail a publish.
- Variants sideloaded with a role filename suffix; attachment meta
  _prautoblogger_image_role + _prautoblogger_base_attachment_id; post
  meta _prautoblogger_og_image_id (frozen for the rebuilt SEO stage) +
  _prautoblogger_square_image_id. No cost-tracker rows ($0 local stage;
  duration logged on the image_composer channel).
- New Images settings: compose_enabled ('1'), compose_variants
  ('og,square'), featured_mark_enabled ('1') — read at point of use.
  Geometry ships as Layout defaults behind the
  prautoblogger_image_compose_layout filter.
- Vendored brand rasters (assets/brand) + bundled OFL Poppins faces
  (assets/fonts) for per-environment byte-stable output (stripImage +
  PNG date/time chunks excluded). Validated on Hostinger PHP 8.3.30 /
  ImageMagick 7.1.1-43: php -l clean on all touched files, double
  render byte-identical (sha256), exact variant geometry.
- Fix: featured/Image B alt text is the editorial caption (was the
  model name); model still persists in _prautoblogger_image_model.
- Image_Attacher extracted from Image_Pipeline (300-line compliance);
  sideloader gains an optional filename suffix param (back-compat '').
- Version 0.16.0 -> 0.17.0 + CHANGELOG + ARCHITECTURE.md #21 +
  CONVENTIONS.md composer guide in this commit. Unit tests: layout
  clamp boundaries, capability ladder, cache invalidation, attacher
  meta-linking, pipeline integration, imagick determinism (gated).

Agent-Session: engineer-prautoblogger-image-composer-20260611

includes/admin/class-settings-fields-extended.php

@@ -258,6 +258,30 @@ class PRAutoBlogger_Settings_Fields_Extended {
 				'default'     => '1',
 				'description' => __( 'When the provider rejects an image prompt as NSFW, retry once with a generic fallback scene built from the article title. Disable to fail fast if the filter gets trigger-happy.', 'prautoblogger' ),
 			),
+			array(
+				'id'          => 'prautoblogger_image_compose_enabled',
+				'label'       => __( 'Compose Branded Variants', 'prautoblogger' ),
+				'type'        => 'toggle',
+				'section'     => 'prautoblogger_images',
+				'default'     => '1',
+				'description' => __( 'Render branded social variants (teal band, logo, baked caption) from each generated image via the local deterministic composer. Auto-degrades to plain resizing or pass-through if the server lacks an image library — publishing is never blocked.', 'prautoblogger' ),
+			),
+			array(
+				'id'          => 'prautoblogger_image_compose_variants',
+				'label'       => __( 'Composed Variant Set', 'prautoblogger' ),
+				'type'        => 'text',
+				'section'     => 'prautoblogger_images',
+				'default'     => 'og,square',
+				'description' => __( 'Comma-separated variants to render for Image A. Supported: og (1200×630 social share), square (1080×1080 card). Unknown values are ignored.', 'prautoblogger' ),
+			),
+			array(
+				'id'          => 'prautoblogger_image_featured_mark_enabled',
+				'label'       => __( 'Featured Image Corner Mark', 'prautoblogger' ),
+				'type'        => 'toggle',
+				'section'     => 'prautoblogger_images',
+				'default'     => '1',
+				'description' => __( 'Overlay a small semi-transparent Peptide Repo mark in the bottom-right corner of featured images, so scraped or re-shared images carry attribution.', 'prautoblogger' ),
+			),
 			array(
 				'id'          => 'prautoblogger_runware_model_catalog',
 				'label'       => __( 'Runware Model Catalog', 'prautoblogger' ),