Fix SSRF, XSS, dedup, force-post, and DB hot-path issues

- Add internal/safehttp: hardened HTTP client (DNS-resolved dial guard
  blocking loopback/RFC1918/CGNAT/link-local, redirect re-validation,
  body-size cap) and rewire article/feed/thumb clients through it
- Cap goquery body at 5 MiB so a hostile origin can't OOM the process
- search.js: reject non-http(s) hrefs to block stored XSS via javascript:
- dedup: tracking-param key "CMP" was unreachable (lookup lowercases);
  fixed to "cmp" so CMP= is actually stripped from canonical URLs
- ForcePost: postItem now returns bool; on dedup-skip ForcePost returns
  false so !post falls back to DB lookup instead of silently consuming
- Bound reaction callbacks behind an 8-slot semaphore; drop overflow
- Add stories indexes on (channel, classified, seen_at DESC),
  (classified, seen_at DESC), and partial image_url to kill full scans
  in IsKnownImageURL and ORDER BY seen_at hot paths
- Surface FTS5 probe Scan error instead of swallowing it

internal/web/static/js/search.js

@@ -40,6 +40,15 @@
       .replace(/'/g, "'");
   }
 
+  // safeURL rejects any href whose scheme isn't http(s). Stored article_url
+  // comes from feeds we don't control; a hostile feed publishing
+  // `javascript:fetch(...)` would otherwise execute on click.
+  function safeURL(s) {
+    const raw = String(s == null ? "" : s).trim();
+    if (/^https?:\/\//i.test(raw)) return raw;
+    return "";
+  }
+
   function render(results) {
     items = results || [];
     activeIndex = items.length > 0 ? 0 : -1;
@@ -55,8 +64,10 @@
            </div>`
         : `<div class="hidden sm:flex w-20 h-20 shrink-0 items-center justify-center rounded-2xl bg-[color:var(--ink)]/5 text-2xl">${escapeHTML(r.channel_emoji || "·")}</div>`;
       const postedRing = r.posted ? ` border-theme-${escapeHTML(r.channel_theme)}` : "";
+      const href = safeURL(r.article_url);
+      if (!href) return "";
       return `
-        <a href="${escapeHTML(r.article_url)}" target="_blank" rel="noopener noreferrer"
+        <a href="${escapeHTML(href)}" target="_blank" rel="noopener noreferrer"
            data-idx="${i}"
            class="search-result group flex items-start gap-4 rounded-2xl p-3 transition border-2 border-transparent hover:bg-[color:var(--ink)]/5${postedRing}">
           ${thumb}
@@ -138,7 +149,8 @@
     } else if (e.key === "Enter") {
       if (activeIndex >= 0 && items[activeIndex]) {
         e.preventDefault();
-        window.open(items[activeIndex].article_url, "_blank", "noopener");
+        const href = safeURL(items[activeIndex].article_url);
+        if (href) window.open(href, "_blank", "noopener");
       }
     }
   });