chore(security): ignore unfixed CVEs in Trivy, override deepmerge-ts (#1085)

Stable twin of #1083, scoped to what exists on this branch.

docker-build.yml — set ignore-unfixed on both Trivy steps. Stable has
the backend and frontend legs only (no aio, no ml), so two steps here
against four on main. Base-image CVEs with no released fix are not
actionable: the Dockerfiles already run `apt-get upgrade -y` behind a
CACHEBUST, so a fix lands in the next build automatically. Reporting
them buries anything someone can actually act on.

backend — deepmerge-ts <8.0.0 has a stack-exhaustion advisory
(CVE-2026-40345, high) reached via mailparser -> html-to-text, which
pins ^7.1.5 so npm cannot get there alone. Stable carries the same
mailparser ^3.9.9 and the same 3-high exposure as main. Not reachable
in our code: html-to-text only feeds deepmerge-ts its options object,
never parsed email content. npm audit on this branch goes 3 high -> 0.

The ml/Dockerfile half of #1083 has no counterpart here — the face
sidecar does not exist on stable, so there is nothing to drift.

Verified on stable itself rather than assuming main's results carry:
npm audit 3 high -> 0, html-to-text exercised end-to-end through
simpleParser, and jest at 1577 passed. The 5 failing suites (20 tests)
fail identically on clean origin/stable with these changes stashed.

Co-authored-by: Paul Nothaft <[email protected]>

backend/package-lock.json

@@ -1,12 +1,12 @@
 {
   "name": "picpeak-backend",
-  "version": "3.45.14",
+  "version": "3.46.0",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "picpeak-backend",
-      "version": "3.45.14",
+      "version": "3.46.0",
       "dependencies": {
         "@aws-sdk/client-s3": "^3.850.0",
         "@aws-sdk/lib-storage": "^3.850.0",
@@ -5315,9 +5315,19 @@
       }
     },
     "node_modules/deepmerge-ts": {
-      "version": "7.1.5",
-      "resolved": "https://registry.npmjs.org/deepmerge-ts/-/deepmerge-ts-7.1.5.tgz",
-      "integrity": "sha512-HOJkrhaYsweh+W+e74Yn7YStZOilkoPb6fycpwNLKzSPtruFs48nYis0zy5yJz1+ktUhHxoRDJ27RQAWLIJVJw==",
+      "version": "8.0.1",
+      "resolved": "https://registry.npmjs.org/deepmerge-ts/-/deepmerge-ts-8.0.1.tgz",
+      "integrity": "sha512-szCXE7YLCvLKR9bFPJcvsezOShdalctSvrgN/LM/QGUEPZQajwjmsMObZ6/DuANT5lxzM/wtO8Feubwdkz8myA==",
+      "funding": [
+        {
+          "type": "ko-fi",
+          "url": "https://ko-fi.com/rebeccastevens"
+        },
+        {
+          "type": "tidelift",
+          "url": "https://tidelift.com/funding/github/npm/deepmerge-ts"
+        }
+      ],
       "license": "BSD-3-Clause",
       "engines": {
         "node": ">=16.0.0"