feat(analysis): vision client + system prompt + AnalysisConfig

The OpenAI-compatible vision client and the bounded prompt/output handling
for the analysis worker (no DB, fully unit-tested):

- analysis::prompt: terse system prompt carrying the JSON schema, the OCR
  kind / content-warning vocabularies, and the output-size caps.
- analysis::vision: VisionClient (downscale via the new `image` dep →
  base64 data-URL → chat/completions with an image_url part), plus pure
  parse_chat_completion (fence/prose-tolerant) and sanitize (drop empty
  OCR, truncate, clamp tags to 10 via the shared page-tag normalizer,
  filter unknown warnings).
- config::AnalysisConfig extended with endpoint/model/api_key/timeouts/
  max_tokens/max_image_dim/max_image_bytes + from_env.
- Deps: add `image` (jpeg/png/webp), reqwest `json` feature. Expose
  api::page_tags::normalize_tag as pub(crate) for reuse.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/package.json

@@ -1,6 +1,6 @@
 {
   "name": "mangalord-frontend",
-  "version": "0.66.0",
+  "version": "0.67.0",
   "private": true,
   "type": "module",
   "scripts": {