ci: re-fix CodeQL #32 + repair loadtest f5-mock build context

Two unrelated CI failures from run #25305811340; fixed in one
commit since neither needs the other to land first.

CodeQL alert #32 (go/log-injection at middleware.go:68) reopened
after b0fc067. The previous fix introduced a scrubLogValue helper
backed by strings.NewReplacer; CodeQL's taint tracker only
recognizes the literal strings.ReplaceAll pattern as a sanitizer
(matches the OWASP example in the rule docs). Wrapper helpers and
NewReplacer don't trigger the recognition, so the analyzer kept
flagging.

Fix: drop the helper. Inline strings.ReplaceAll chains directly at
the call site for r.Method and r.URL.Path. Same runtime semantics
(strip CR/LF/NUL); CodeQL pattern-matches the literal call so the
alert can finally close.

Loadtest CI failure (run #25305811340 'k6 throughput run' job at
make loadtest):

  ERROR: failed to compute cache key: failed to calculate checksum
  of ref ...: "/deploy/test/f5-mock-icontrol": not found

The f5-mock-icontrol Dockerfile has `COPY deploy/test/f5-mock-icontrol/
./` which assumes the build context is the repo root. The
docker-compose.test.yml f5-mock-icontrol service correctly uses the
long-form build:

  build:
    context: ..        # = repo root from deploy/docker-compose.test.yml
    dockerfile: deploy/test/f5-mock-icontrol/Dockerfile

The loadtest compose at deploy/test/loadtest/docker-compose.yml
used the shorthand:

  build: ../f5-mock-icontrol

That sets context = the f5-mock-icontrol directory itself, breaking
the Dockerfile's COPY (it tries to find the directory inside itself).

Fix: change the loadtest compose to the long-form pattern matching
docker-compose.test.yml, with context: ../../.. (= repo root from
deploy/test/loadtest/) and explicit dockerfile path.

Verified locally:
  gofmt: clean.
  go vet ./internal/api/middleware/...: exit 0.
  go test -short -count=1 ./internal/api/middleware/...: ok 0.253s.
  python3 -c 'import yaml; yaml.safe_load(...)' on the compose
    file: parses clean.
  grep -rnE 'scrubLogValue' internal/api/: zero references (helper
    fully dropped).

References:
  https://github.com/certctl-io/certctl/security/code-scanning/32
  CI run https://github.com/certctl-io/certctl/actions/runs/25305811340
Closes CodeQL #32 + restores loadtest CI.

deploy/test/loadtest/docker-compose.yml

@@ -290,7 +290,15 @@ services:
   # /healthz endpoint.
   # ---------------------------------------------------------------------------
   f5-mock-target:
-    build: ../f5-mock-icontrol
+    # Long-form build to match docker-compose.test.yml: the Dockerfile
+    # has `COPY deploy/test/f5-mock-icontrol/ ./` which assumes the
+    # build context is the REPO ROOT. The previous shorthand form
+    # `build: ../f5-mock-icontrol` set the context to the
+    # f5-mock-icontrol directory itself, breaking the COPY at CI build
+    # time (run #25305811340: "deploy/test/f5-mock-icontrol: not found").
+    build:
+      context: ../../..
+      dockerfile: deploy/test/f5-mock-icontrol/Dockerfile
     container_name: certctl-loadtest-f5-mock
     healthcheck:
       test: ["CMD-SHELL", "wget -q -O- http://localhost:8080/healthz || exit 1"]