300+ Source Newsroom Expansion, Inverted-Index Story Clustering & Feed Link Fixes

• 🗞️ 300+ Source Newsroom Catalog Across All 6 Topic Desks: Added 210 live-verified RSS and Atom feeds across AI & Frontier Tech, Apple & Devices, Politics & Policy, Venture & Big Tech, Engineering & Security, and Indie Web & Culture (~50+ sources per desk) while keeping user-facing Classic RSS Starter Bundles cleanly curated at 10–12 feeds per pack.
• ⚡ Inverted-Index Story Clustering & Multi-Section Publisher Deduplication: Lifted the newsroom clustering pool to 3,000 articles with exact inverted-index token/bigram candidate pruning, added 60-second watermark-backed edition caching, collapsed multi-section outlet feeds by canonical publisher so sibling sections never self-cluster, and introduced tiered background polling and 50-article retention for unsubscribed newsroom feeds.
• 🔗 Authentic Publisher URLs Only in Webnerd News & Studio: Removed synthetic starter-pack and Studio placeholder seed items and added automatic startup database cleanup so story clusters exclusively highlight live crawled publisher links.
• 📡 Atom & RSS Alternate Link Indexing: Updated feed XML link selection to prioritize rel="alternate" HTML permalinks over Atom rel="replies" (/comments/default) and rel="self" feed URLs, automatically healing previously affected Blogger and RSS entries.
• 🧭 Outbound URL Reconciliation & Malformed Link Repair: Repaired double-origin URL concatenations, resolved podcast episodes without per-item links to their canonical show pages instead of '#', and hid Open Original controls when no external URL exists.
• 🔐 Webnerd News Sign-In & Frontend DOM Guardrails: Fixed the handle/email input binding on password sign-in, added safe return_to web redirects on fallback Google sign-in, and extended pre-deploy static DOM checks across /labs/news and /auth/mobile.
• 📤 Classic RSS Sharing & /via webnerd.ai Intents in Webnerd News: Added Share controls and the 's' keyboard shortcut across Webnerd News cards, Live Wire, Full Coverage, and the Article Reader—publishing to Webnerd Shared Items (with notes, highlighted quotes, and optional Bluesky OAuth cross-posting) for signed-in readers and opening downstream Bluesky, X, Facebook, LinkedIn, and Copy flows with '/via webnerd.ai' attribution and direct publisher URLs for everyone.