fix(platform): unwrap integration list envelope so issue desk shows issues

[larryro]

What

The issue desk rendered no issues even when untracked GitHub issues existed.

executeIntegration returns an envelope whose connector payload — the issues array plus the upstream "is there a next page" hint — lives under .result:

{ name, operation, result: { data, pagination, ... }, ... }

listUntrackedGitHubIssues read res.data / res.pagination from the top level, which always resolved to undefined → an empty page with no next page → the filtered list collapsed to nothing.

Fix

Extract a shared readIntegrationListPage helper that:

• unwraps .result first (mirroring the client's parsePage),
• tolerates an already-flat { data, pagination } payload for forward compatibility (a future connector that returns the payload directly still works),
• degrades to an empty, terminal page on a malformed/null result.

listUntrackedGitHubIssues now delegates to it instead of reading the top level.

Tests

New integration_list_page.test.ts covers the nested envelope, the hasNext signal, the regression shape (top-level data must be ignored), the forward-compatible flat shape, and malformed input. All 5 pass.