Newsreader: auto-fetch full article text for truncated RSS entries

Many RSS feeds only syndicate a snippet and require visiting the website for the full article. The newsreader should detect truncated feed entries (short <description> + a <link>) and auto-fetch the full article content using a Readability-style extractor (e.g. Mozilla Readability.js or FiveFilters Full-Text RSS approach). This makes the reader self-contained and avoids the ad-impression dark pattern. Details: 1) Detect truncation heuristic (description length < threshold, or presence of 'read more' patterns). 2) Fetch the linked page. 3) Run through Readability/content extractor to strip nav/ads. 4) Store full text alongside the feed entry. 5) Rate-limit fetches; respect robots.txt. 6) Fallback gracefully to snippet if fetch fails.