fix(agent): disable seahorse context manager on freebsd/arm (#2417)

* fix(agent): disable seahorse context manager on freebsd/arm

Exclude freebsd/arm from the seahorse-enabled build and route it to the
unsupported stub implementation.

This avoids freebsd/arm build failures caused by modernc sqlite/libc while
keeping picoclaw buildable on that target.

* build: bump Go version from 1.25.8 to 1.25.9

* ci: install and run govulncheck directly in PR workflow

.github/workflows/pr.yml

@@ -41,10 +41,11 @@ jobs:
         with:
           go-version-file: go.mod
 
+      - name: Install govulncheck
+        run: go install golang.org/x/vuln/cmd/govulncheck@v1.1.4
+
       - name: Run Govulncheck
-        uses: golang/govulncheck-action@v1
-        with:
-          go-package: ./...
+        run: govulncheck -C . -format text ./...
 
   test:
     name: Tests