[Gusto R1] Add shared policy, route, and connection constants

[yuwenmemon]

Add the foundational constants, types, routes, and utility helpers that all three Gusto releases depend on.

Parent Issues: Expensify/App#85850, Expensify/Expensify#591910
Design Doc Section: Detailed — Add the shared policy, route, and connection

Files to update

• src/CONST/index.ts — Add CONST.POLICY.CONNECTIONS.NAME.GUSTO, user-facing names, route keys, and Gusto-specific sync stage names. Add a grouping helper so accounting-only code can explicitly filter out HR integrations.
• src/types/onyx/Policy.ts — Extend Connections with a gusto entry, add the Gusto config/data types, add isHREnabled, and extend PolicyConnectionSyncProgress with an optional result payload for the sync results modal.
• src/libs/API/types.ts — Add the GustoSyncResult type to be used by the sync progress object and the results modal.
• src/SCREENS.ts — Add screen IDs for the HR page and the two Gusto settings pages.
• src/ROUTES.ts — Add WORKSPACE_HR, WORKSPACE_HR_GUSTO_APPROVAL_MODE, and WORKSPACE_HR_GUSTO_FINAL_APPROVER.
• src/libs/Navigation/AppNavigator/Navigators/WorkspaceSplitNavigator.tsx — Register the new screens in the workspace settings navigator.
• src/libs/Navigation/linkingConfig/config.ts — Add deep-link support for the new HR routes.
• src/libs/Navigation/linkingConfig/RELATIONS/WORKSPACE_TO_RHP.ts — Add relations so the right-hand pane stack works like other workspace settings pages.
• src/libs/API/parameters/EnablePolicyHRParams.ts — New API parameter type for toggling the HR feature.
• src/libs/API/parameters/OpenPolicyHRPageParams.ts — New API parameter type for fetching the HR page payload on mount.
• src/libs/API/parameters/ConnectPolicyToGustoParams.ts — New API parameter type for the OAuth connect command.
• src/libs/API/parameters/SyncGustoParams.ts — New API parameter type for manual sync.
• src/libs/API/parameters/UpdateGustoApprovalModeParams.ts — New API parameter type for the approval mode setting.
• src/libs/API/parameters/UpdateGustoFinalApproverParams.ts — New API parameter type for the final approver setting.
• src/libs/API/parameters/index.ts — Export the new parameter types.
• src/libs/actions/Policy/Policy.ts — Add enablePolicyHR() with the usual optimistic Onyx updates.
• src/libs/actions/PolicyConnections.ts — Add openPolicyHRPage() beside openPolicyAccountingPage() so the new HR page can fetch its initial payload through the same workspace-connections layer.
• src/libs/PolicyUtils.ts — Add basic Gusto helpers like isGustoConnected() and split shared connection helpers into accounting vs HR buckets.
• src/libs/ReportActionsUtils.ts — Route Gusto sync-failure recovery back to the HR page instead of the Accounting page.
• src/libs/ReportUtils.ts — Add Gusto icon/name support anywhere shared integration helpers need it.
• src/pages/workspace/accounting/PolicyAccountingPage.tsx — Explicitly filter to accounting-only connection names so Gusto never appears here.
• src/pages/workspace/WorkspaceInitialPage.tsx — Add the new HR row and avoid showing accounting red-brick-road signals for Gusto sync failures.
• src/languages/en.ts — Add HR page labels, Gusto-specific strings, and sync-stage copy.

Key implementation details

• Add a new policy feature flag isHREnabled.
• Keep Gusto in policy.connections — do not create a separate Onyx key.
• Show the HR row in the workspace LHN when policy.isHREnabled || policy.connections.gusto. This makes already-connected workspaces visible even if the feature flag was never turned on manually.
• Keep the Accounting page unchanged from the user's point of view. Gusto should never get a slot there.

Issue Owner

Current Issue Owner: @ShridharGoel

[melvin-bot]

Triggered auto assignment to Design team member for new feature review - @dannymcclain (NewFeature)