Pi-hole records: mount addn-hosts into FTL hostsdir, not dnsmasq.d

FTL's generated dnsmasq.conf has no conf-dir: /etc/dnsmasq.d/ is never
read (the 2026-08-24 scratch-name test proved the file was inert; names
only resolved from the query cache). The only file-based local-record
mechanism is hostsdir=/etc/pihole/hosts. Mount the record file there.
Doc: record the pitfall in Pi-hole.md.

tests/pihole.bats

@@ -40,8 +40,12 @@ HOSTS="$PIHOLE_DIR/addn-hosts"
     grep -q '^EnvironmentFile=/home/dank/Containers/pihole/env$' "$QUADLET"
 }
 
-@test "the pihole quadlet mounts the addn-hosts record file read-only" {
-    grep -qE '^Volume=/home/dank/Containers/pihole/addn-hosts:/etc/dnsmasq\.d/addn-hosts:ro$' "$QUADLET"
+@test "the pihole quadlet mounts the addn-hosts record file into the FTL hostsdir" {
+    # FTL (a dnsmasq fork) does not read /etc/dnsmasq.d/ (the generated
+    # dnsmasq.conf has no conf-dir). Its only file-based local-record
+    # mechanism is hostsdir=/etc/pihole/hosts (each file parsed as an
+    # /etc/hosts file). Mount the record file there, read-only.
+    grep -qE '^Volume=/home/dank/Containers/pihole/addn-hosts:/etc/pihole/hosts/addn-hosts:ro$' "$QUADLET"
 }
 
 @test "the pihole env example has placeholder values only" {