feat(agent): extract HF widget gallery images into civitai.images with recommended dimensions

- Add extract_gallery_images() to parse YAML widget entries from README
  frontmatter, convert relative image URLs to absolute HF URLs, and
  build civitai.images-compatible entries with prompt metadata
- LLM now extracts recommended_width/recommended_height from README
  (e.g. "Best Dimensions"), used as gallery image dimensions
- extract_gallery_images() accepts default_width/height parameters,
  falling back to 512x512 when LLM provides no recommendation
- Frontend ShowcaseView.js: defensive NaN guard for 0 width/height
- post_processor: consistently merge civitai updates across triggers,
  description, and gallery blocks with distinct variable names
- SKILL.md: add recommended_width/recommended_height to output schema
- 62 tests pass, including gallery extraction and dimension tests

py/services/agent/skills/enrich_hf_metadata/SKILL.md

@@ -78,6 +78,9 @@ Sources to consider:
 
 Return empty array if no meaningful content tags remain after filtering.
 
+### recommended_width, recommended_height
+The recommended image generation resolution for this model, in pixels. Look for sections like "Best Dimensions", "Recommended size", "Suggested resolution", or similar phrasing in the README. Prefer the explicitly marked "Best" or default resolution. If the table/list has multiple entries (e.g. "768 x 1024 (Best)" and "1024 x 1024 (Default)"), use the one marked "Best". Return integers. If no resolution can be determined, return 0 for both.
+
 ### preview_url
 The URL of the most suitable preview image from the README. Look for image tags (e.g. `![alt](url)`) and the YAML frontmatter `widget:` section (which often has `output.url` fields). Choose the first image that appears to be a generation example (not a logo or diagram). Construct the absolute URL as `https://huggingface.co/{{repo}}/resolve/main/{filename}`. If no suitable image is found, return an empty string.
 
@@ -98,6 +101,8 @@ Return ONLY a JSON object with exactly these fields (no markdown fences, no extr
   "trigger_words": ["<word1>", "<word2>"],
   "short_description": "<1-2 sentence summary>",
   "tags": ["<tag1>", "<tag2>"],
+  "recommended_width": 768,
+  "recommended_height": 1024,
   "preview_url": "<image URL or empty string>",
   "confidence": "<high|medium|low>"
 }