v3.2.6-sr94.17: QR clipboard and admin search fixes

Community-inspired improvements

• Copy a PNG from the authenticated QR page at the selected resolution. Permission denial, conversion failure and unsupported browsers retain PNG/SVG download and print fallback. No clipboard reading or remote QR service.
• Fix numeric-starting email searches in both administrator link and domain tables. Rows and totals share one strict numeric-ID/email filter, including pagination and malformed/oversized input handling. Authorization is unchanged.

Credit: kkpanfilov, PR #1016 and utkarshr3144, PR #1034. These are adapted implementations, not blind merges of older code or unrelated lockfile changes. The review guide records other proposals and reasons for deferral.

Validation and compatibility

• Release CI: full isolated migration/API/security regressions, configuration checks, fresh Redis visit-worker/restart tests and exact image publication passed. Main CI passed too.
• Desktop/mobile Chromium: independent decoding of copied PNG and PNG/SVG downloads, permission/conversion failure, overlapping clicks, retry, unsupported controls, print/PDF, image recovery, numeric-email admin search and unchanged visit counts passed.
• Browser clipboard writes are intercepted in tests; no operator clipboard is changed. Physical iPhone/Safari clipboard acceptance is not claimed.
• No migration, data rewrite, new secret or runtime dependency. Keep existing authentication/WAF protections. Deployment/backup acceptance is separately recorded in the review and homelab recovery documentation; do not deploy solely because CI passed.

The completed original roadmap remains in upstream PR #1046; this small follow-up is separate from that review branch.