feat(frontend): room occupancy + invoice-to-client checkout and workspace task unification

[ghost]

PR Checklist

• The PR title follows our guidelines.
• There is an issue for the bug/feature this PR is for.
• All existing tests and lints pass.

What is the current behavior?

• Room/unit pickers offer occupied beds; nothing distinguishes an active-admission unit from a free one.
• No send-to-client checkout; POST /:invoiceId/checkout-session runs without a billing-edit permission check.
• Lines already paid on a past invoice can be re-seeded onto the editable bill and charged again.
• Workspace Schedule and the Tasks panel hold separate state (local-only duplicates possible); completed schedule rows disappear on refresh.
• Chat appointment header has no lifecycle actions; the forms builder shows no summary for multi-task templates.
• Sonar smells: nested ternaries in InvoiceStep.tsx / lib/forms.ts, duplicate @yosemite-crew/types imports in DocumentsPanel.tsx. Two broken reporoster.com image embeds in the README.

What is the new behavior?

1. Room-unit occupancy (backend + types + frontend)

• backend/room-unit.service.ts: getOccupiedUnitIds() queries active, non-discharged admissions with a unitId; toDomain() sets isOccupied and list results are enriched per org (service test updated).
• types/roomUnit.ts: optional isOccupied with room-unit-occupied FHIR extension in toFHIRRoomUnit/fromFHIRRoomUnit.
• New features/appointments/lib/roomUnitAvailability.ts (isAssignableRoomUnit, getAssignableRoomUnits, getFirstAssignableRoomUnitId, toAssignableRoomOptions) — treats a unit as assignable unless occupied (a unit keeps its own current occupant). Consumed by ChangeRoom, AppointmentWorkspace, InpatientSchedule, and workspace services/store.

2. Invoice → client checkout & double-bill safety (backend + frontend)

• backend/invoice.router.ts: checkout-session route now requires withInvoiceOrgPermissions() + requirePermission("billing:edit:any") (router test updated).
• billing/invoiceService.ts: new sendInvoiceToClient(invoiceId) returning { checkout, emailSent }.
• InvoiceStep.tsx: send-to-client flow gated on "Ready for billing"; state-correct payment controls (Abort while checking, Done when confirmed, Abort + Check again when delayed); printInvoice now returns success so a popup-blocked download surfaces instead of failing silently; settled-line guard — any line name on a settled/paid past invoice is excluded from the editable bill regardless of the billed flag.

3. Workspace task/schedule unification

• TreatmentStep.tsx: the task store is the single source of truth for schedule rows (no local duplicates); workspace task load forces includeCompleted so completed rows survive refresh.
• InpatientSchedule.tsx simplified to a template-search + read model; SummaryStep, workspace aggregate/template services, store, and types/workspace.ts updated to match.

4. Chat appointment actions

• ChatContainer.tsx / ChatHeaderContext.tsx: Reschedule, Mark complete (changeAppointmentStatus → COMPLETED with success/error toasts), and Book follow-up from the chat appointment header.

5. Forms task-template summary + UI polish

• FormInfo.tsx: TaskTemplateSummary renders multi-task template blocks (labels resolved from taxonomy); AddForm Details/Review/index and lib/forms.ts / taskService.ts normalize task-block instructions.
• CompanionsTable.tsx + DataTable.css, UserHeader.tsx (route-change reset moved into an effect to avoid cross-component render warning).

6. Cleanup

• Sonar: flattened nested ternaries (InvoiceStep.tsx, lib/forms.ts), deduped type imports (DocumentsPanel.tsx).
• README: removed Release Versioning (kept in apps/frontend/README.md); replaced broken reporoster.com image embeds with working GitHub stargazer/forker links.
• ~25 __tests__ files added/updated across all workstreams.

Related Issue(s)

Fixes #1748

Validation performed

• npx tsc --noemit (frontend) — clean.
• Targeted Jest: workspace steps, panels, room-unit availability, invoice/workspace/task services, store, forms, tasks, chat, companions.
• Backend room-unit.service and invoice.router suites updated and passing.

Impact area

frontend (appointment workspace, room mgmt, billing, forms, tasks, chat, UI), backend (room-unit service, invoice router), types (roomUnit). Additive shared type; no Merck paths; no breaking changes.

[harshvardhan-yc]

LGTM. Ready to merge