Fetch all pages in piped ListApplications

[rootp1]

What this PR does:

Summary

• paginate PipedAPI.ListApplications internally until the datastore cursor is exhausted
• add a regression test that verifies multi-page application results are fully returned to piped clients

Why we need it:

PipedAPI.ListApplications currently returns only the first datastore page and silently drops additional applications when a piped manages more than one page of apps.

Which issue(s) this PR fixes:

Fixes #7051

What Changed

• replaced the single applicationStore.List call in pkg/app/server/grpcapi/piped_api.go with an internal loop over datastore cursors
• added TestPipedAPIListApplicationsFetchesAllPages in pkg/app/server/grpcapi/piped_api_test.go

Verification

• go test ./pkg/app/server/grpcapi -run TestPipedAPIListApplicationsFetchesAllPages — passed
• go test ./pkg/app/server/grpcapi — passed
• $(go env GOPATH)/bin/golangci-lint run --config .golangci.yml ./pkg/app/server/grpcapi/... — passed
• make check/gen/code — passed
• make check — failed: repository lint step uses golangci-lint v2.4.0 built with Go 1.25, but this repository targets Go 1.26.2, so lint aborts before the test phase
• ./hack/ensure-dco.sh — failed: reports pre-existing commit 25ae69937e55e8330bff96c34346718f3e5e7148 missing Signed-off-by; new commit 5430db3949cb1ef3a5bdb90608629f90e44e24eb is signed off

Scope

• unrelated files were not changed; only the piped ListApplications handler and its focused test were updated

Does this PR introduce a user-facing change?:

• How are users affected by this change: piped clients now receive all registered applications even when the datastore returns multiple pages
• Is this breaking change: no
• How to migrate (if breaking change): not applicable