Add Extra accounts page and invitation management UI

[j-ruda-guardian]

Summary

Adds an Extra accounts MMA page for Digital Plus subscribers (gated by ?TEST_EXTRA_ACCOUNTS_FLAG=true for now)
Adds nav entry, account overview banner, and useExtraAccounts hook + Zustand store
Implements send, cancel, and remove-access flows with confirmation modals and success/error feedback
Moves Modal to client/components/shared with containerCssOverrides and hideCloseButton

Notes

API calls are mocked (2s delay); list refetch uses hardcoded data until backend is ready

###Test plan

• Enable with ?TEST_EXTRA_ACCOUNTS_FLAG=true on a Digital Plus test account
• Send invitation from an empty slot (form validation, loading, success message)
• Cancel a pending invitation via modal
• Remove access from an active account via modal
• Confirm holiday modals still work after the shared Modal move

[Copilot]

Pull request overview

Adds an “Extra accounts” management experience to MMA (currently gated behind a query param + Digital Plus), including navigation entrypoints and invitation lifecycle UI, and centralises the shared Modal component for reuse (holiday flows updated accordingly).

Changes:

• Introduces Extra Accounts page UI (banner, rows, invite form, confirmation modals) plus a useExtraAccounts hook backed by a Zustand store.
• Adds an “Extra accounts” route and nav entries (left nav + dropdown), and wires in an icon + page skeleton metadata.
• Moves Modal into client/components/shared and updates Holiday modals to import it from the new location.

Reviewed changes

Copilot reviewed 20 out of 20 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
client/utilities/hooks/useExtraAccounts.ts	New hook to load/gate extra accounts and handle invite/cancel/remove flows.
client/utilities/extraAccounts.ts	New feature gating helpers (Digital Plus + query param).
client/stores/ExtraAccountsStore.tsx	New Zustand store for extra accounts state + loading/error handling.
client/components/shared/nav/NavConfig.tsx	Adds “Extra accounts” nav item configuration and icon.
client/components/shared/nav/LeftSideNav.tsx	Conditionally renders the new nav item based on eligibility gate.
client/components/shared/nav/DropdownNav.tsx	Conditionally renders the new nav item in dropdown based on eligibility gate.
client/components/shared/Modal.tsx	Enhances shared modal with container CSS overrides + optional close button.
client/components/mma/shared/ExtraAccountsBanner.tsx	Adds an account overview banner CTA linking to extra accounts.
client/components/mma/shared/assets/ExtraAccountsIcon.tsx	Adds the icon used in nav for Extra Accounts.
client/components/mma/MMAPageSkeleton.tsx	Adds page metadata for the /extra-accounts route.
client/components/mma/MMAPage.tsx	Adds lazy-loaded route entry for the Extra Accounts page.
client/components/mma/holiday/HolidayReview.tsx	Switches holiday flow to use the shared Modal import.
client/components/mma/holiday/HolidayQuestionsModal.tsx	Switches holiday flow to use the shared Modal import.
client/components/mma/holiday/HolidayAnniversaryDateExplainerModal.tsx	Switches holiday flow to use the shared Modal import.
client/components/mma/holiday/ExistingHolidayStopActions.tsx	Switches holiday flow to use the shared Modal + HideFunction types.
client/components/mma/extraAccounts/ExtraAccounts.tsx	New main page for managing extra accounts and showing status + feedback.
client/components/mma/extraAccounts/ExtraAccountRow.tsx	New row UI for empty/pending/active slots and associated actions/modals.
client/components/mma/extraAccounts/ExtraAccountInviteForm.tsx	New invite form (email + consent) for empty slots.
client/components/mma/extraAccounts/ExtraAccountCancelInvitationModal.tsx	New reusable confirmation modal wrapper for cancel/remove flows.
client/components/mma/accountoverview/AccountOverview.tsx	Displays the Extra Accounts banner behind the current gate.

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