fix(ci): replace gitleaks-action with manual install

`gitleaks/gitleaks-action@v2` is now paywalled for organisations:
the action errors out with `🛑 missing gitleaks license. Go grab one
at gitleaks.io and store it as a GitHub Secret named
GITLEAKS_LICENSE.` Worse, it cannot reliably detect personal-vs-org
on Gitea (the GitHub API contract differs), so it defaults to
license enforcement and the scan fails. The gitleaks binary itself
remains MIT-licensed and free.

Mirror the pattern we just adopted for Trivy in #45: drop the
wrapper, install the binary directly via curl + tar from the GitHub
release, run the CLI. This:

- removes a third-party action dependency we did not need;
- pins the gitleaks version explicitly;
- harmonises with the Trivy step that lives next to it.

Apply the same change to `.gitea/workflows/security-scheduled.yml`
in the same PR — it had both broken integrations (`trivy-action
@master` plus `gitleaks-action@v2`) and was waiting silently to
fail at next Monday's cron.

Per-PR gitleaks scan uses `--no-git --source .` (working tree only)
since the scan job uses a shallow checkout; the weekly scheduled
job switches to a full clone (`fetch-depth: 0`) and runs gitleaks
in deep-history mode (default), which is the value-add of the
scheduled job over the per-PR gate.

`--redact` is added on both invocations so any matched secret is
masked in the CI log itself (no leak via the log artefact).

Also drop `cache: 'pnpm'` from `actions/setup-node` in the
scheduled workflow — we already removed it from ci.yml in #8 (the
act_runner cache server is unreachable from job containers; every
restore burns ~2 min ETIMEDOUT for zero hits). Consistency.

.gitea/workflows/ci.yml

@@ -116,10 +116,40 @@ jobs:
             --exit-code 1 \
             --severity CRITICAL,HIGH \
             .
-      # Secret scan, same reasoning (gitleaks is a Go binary).
-      - uses: gitleaks/gitleaks-action@v2
+      # Secret scan. Same install pattern as Trivy: gitleaks is a Go
+      # binary, and the official `gitleaks/gitleaks-action@v2` wrapper
+      # is now paywalled for organisations (a GITLEAKS_LICENSE secret
+      # from gitleaks.io is required, otherwise the action errors out
+      # with `🛑 missing gitleaks license`). The binary itself stays
+      # MIT-licensed and free — installing it directly bypasses the
+      # wrapper and gives us version pinning for free.
+      - name: Install gitleaks
         env:
-          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          # Bump deliberately. Same caveat as TRIVY_VERSION above —
+          # not Renovate-tracked out of the box. Releases:
+          # https://github.com/gitleaks/gitleaks/releases.
+          GITLEAKS_VERSION: '8.21.0'
+          GITHUB_TOKEN: ${{ secrets.GITHUBCOM_TOKEN }}
+        run: |
+          curl -sfL \
+            -H "Authorization: Bearer ${GITHUB_TOKEN}" \
+            -o /tmp/gitleaks.tar.gz \
+            "https://github.com/gitleaks/gitleaks/releases/download/v${GITLEAKS_VERSION}/gitleaks_${GITLEAKS_VERSION}_linux_x64.tar.gz"
+          tar -xzf /tmp/gitleaks.tar.gz -C /usr/local/bin gitleaks
+          gitleaks version
+      - name: Run gitleaks
+        # `--no-git --source .` scans the working tree only. The scan
+        # job uses a shallow checkout, so a git-history scan would not
+        # see beyond HEAD anyway; the weekly security-scheduled
+        # workflow does the deep history scan with a full clone.
+        # `--redact` masks any matched secret in the log output so we
+        # do not leak it via the CI logs themselves.
+        run: |
+          gitleaks detect \
+            --no-git \
+            --source . \
+            --redact \
+            --exit-code 1
 
   commits:
     # PRs opened by Renovate (apf-portal-bot) carry commit messages