test: sweep example data in test files to RFC-5737 + placeholders

Mirrors the .md/.txt sweep across all tracked _test.go, testdata XML,
and .http integration files. Test files are self-contained (producer
+ assertion in the same file), so the matched-pair swap stays green
under `go test ./...`.

Mapping applied:
  192.168.178.[0-9]+   → 192.0.2.[same]
  192.168.1.[0-9]+     → 192.0.2.[same]
  Sound Machinechen    → Living Room SoundTouch
  A Sound Machine      → Kitchen SoundTouch
  A81B6A536A98 + case/separator variants → AABBCCDDEEFF (etc.)
  A81B6A849D99         → AABBCCDDEE01
  A81B6A849D88         → AABBCCDDEE03
  A81B6A536A09         → AABBCCDDEE04
  884AEAEEBD27         → AABBCCDDEE02
  3230304              → 1000001
  9569497              → 1000002

Two semantic fixes alongside the bulk swap:

- pkg/service/zeroconf/zeroconf_test.go: the "private 192" and
  "strips query" cases pin acceptance of RFC-1918 192.168/16. They
  must use a real 192.168 value; doc-range IPs would (correctly) be
  rejected by validateZcBaseURL. Switched to 192.168.10.10 — generic
  enough not to match any home LAN default, real enough for the
  validator. Added a comment explaining why this single test still
  carries a 192.168 literal.

- pkg/service/setup/setup_test.go: TestTestDNSRedirection mocks the
  device's `od -An -tu1` byte output, which is space-separated
  octets ("192 168 1 100"). My sed only matched the dot-separated
  form, so the mock was returning the old IP while the test
  assertions had moved to the doc range. Updated to " 192 0 2 100".

go build ./... clean. go test ./... clean (only TestDocsConsistency
remains failing, which is a pre-existing/untracked-file issue).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

pkg/client/testdata/sources_response.xml

@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="UTF-8" ?>
-<sources deviceID="A81B6A536A98">
+<sources deviceID="AABBCCDDEEFF">
     <sourceItem source="AUX" sourceAccount="AUX" status="READY" isLocal="true" multiroomallowed="true">AUX IN</sourceItem>
     <sourceItem source="AIRPLAY" sourceAccount="AirPlayUserName" status="UNAVAILABLE" isLocal="false" multiroomallowed="false">AirPlayUserName</sourceItem>
     <sourceItem source="QPLAY" sourceAccount="QPlay1UserName" status="UNAVAILABLE" isLocal="true" multiroomallowed="true">QPlay1UserName</sourceItem>