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/ingestion/parser.go

@@ -4,7 +4,6 @@ import (
 	"context"
 	"html"
 	"log/slog"
-	"net/http"
 	"regexp"
 	"strconv"
 	"strings"
@@ -12,11 +11,13 @@ import (
 
 	"github.com/mmcdole/gofeed"
 	ext "github.com/mmcdole/gofeed/extensions"
+
+	"pete/internal/safehttp"
 )
 
 const userAgent = "Pete/1.0 (newsbot; +https://github.com/reala-misaki/pete)"
 
-var feedClient = &http.Client{Timeout: 30 * time.Second}
+var feedClient = safehttp.NewClient(30 * time.Second)
 
 // FeedItem represents a parsed RSS item ready for routing.
 type FeedItem struct {