Read a web page when he names one, and watch a few on a timer (#259)

The network fallback behind the local sources, off unless configured.

internal/crawl is pure: a stdlib robots.txt parser (group specificity,
wildcards, Crawl-delay, cached per host), HTML-to-plaintext extraction, and a
watcher that notes a watched page only when its text changed. It has no store
access and no net/http; cmd/mavend/crawls.go is the impure half.

Every limit is code and tested: the guarded fetcher from #258 enforces the host
allowlist/denylist, refuses private addresses in the dialer Control hook (so DNS
rebinding and each redirect hop are covered), caps size and redirects, times out,
and spaces requests per host. A robots.txt Disallow is refused with no override.

On demand, reading is a query source placed last in the chain, after his memory,
his notes, and the local Kiwix ZIMs once those are wired: no URL in the
utterance means no fetch, and only the URL ever leaves the box. Scheduled
watches write notes and announce nothing.

The vendored tree has no x/net/html, goquery or temoto/robotstxt, so the parsers
are stdlib. No new dependency.

cmd/mavend/main.go

@@ -171,6 +171,7 @@ func run(args []string) error {
 		factWorker *factEnrichmentWorker
 		evalWorker *memoryEvalWorker // nil ⇒ memory evaluation off (the default)
 		feedWkr    *feedWorker       // nil ⇒ no feed is read (the default)
+		crawlWkr   *crawlWorker      // nil ⇒ no page is watched (the default)
 	)
 
 	if !locked {
@@ -267,6 +268,7 @@ func run(args []string) error {
 		factWorker = newFactEnrichmentWorker(st, eco, time.Duration(cfg.FactEnrichmentInterval))
 		evalWorker = newMemoryEvalWorker(st, phr, cfg)
 		feedWkr = newFeedWorker(ipc.NewStoreAPI(st), embedderOf(voiceW), cfg)
+		crawlWkr = newCrawlWorker(newCrawler(cfg), ipc.NewStoreAPI(st), embedderOf(voiceW), cfg)
 
 		coreAPI = &daemonAPI{
 			CoreAPI:          ipc.NewStoreAPI(st),
@@ -454,6 +456,7 @@ func run(args []string) error {
 			factWorker = newFactEnrichmentWorker(st, eco, time.Duration(cfg.FactEnrichmentInterval))
 			evalWorker = newMemoryEvalWorker(st, phr, cfg)
 			feedWkr = newFeedWorker(ipc.NewStoreAPI(st), embedderOf(voiceW), cfg)
+			crawlWkr = newCrawlWorker(newCrawler(cfg), ipc.NewStoreAPI(st), embedderOf(voiceW), cfg)
 
 			// Swap the CoreAPI from the locked placeholder to the real store adapter.
 			newAPI := &daemonAPI{
@@ -506,6 +509,13 @@ func run(args []string) error {
 				}()
 			}
 
+			// Start the watched-page crawls (nil unless configured).
+			if crawlWkr != nil {
+				go func() {
+					crawlWkr.run(ctx)
+				}()
+			}
+
 			dl.unlock()
 			log.Printf("mavend: unlocked via passkey assertion")
 			return nil
@@ -558,6 +568,13 @@ func run(args []string) error {
 				feedWkr.run(ctx)
 			}()
 		}
+		if crawlWkr != nil {
+			wg.Add(1)
+			go func() {
+				defer wg.Done()
+				crawlWkr.run(ctx)
+			}()
+		}
 	}
 
 	<-ctx.Done()