feat(messages): unified conversation inbox — connect demand ↔ supply, offers reach the seeker

Phase 1 of the messaging rework: one conversation/thread model (Inquiry) is the single source of truth, read perspectivally by both sides.

- domain/inquiry: add kind (INQUIRY|OFFER), tenantOrgId (demand org), offeredPropertyIds
- provider/service: InquiryFilters gains tenantOrgId+kind; new createInquiry (demand→supply) & createOffer (supply→demand) materialize threads; addMessage bumps unread; reply carries senderType (tenant vs supply_user)
- hooks: useCreateInquiry, useCreateOffer; reply payload carries sender perspective
- demand: InquiryQuickDialog → createInquiry via provider (session-based tenant/org, no hardcode); Anfragen.tsx reads via React Query (tenantOrgId) with Gesendet/Erhalten tabs, replies via provider, shows offered properties for OFFER threads; inquiryStore reduced to dialog-only (removes Zustand server-data island)
- supply: OfferChatComposer send now materializes an OFFER conversation into the seeker's inbox (routed via latentNeed.tenantOrgId); Anfragencenter gains a "Gesendet" tab; ActiveInquiriesTab filters by perspective (org + kind)
- seed: merge demand inquiries with tenantOrgId=org-mobimo + 2 OFFER seeds; provider seeds from both sets

Closes the loop: a sent inquiry reaches the Verwaltung and a sent offer reaches the Nachfrager — both answerable in one thread.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/domain/latentNeed.ts

@@ -5,6 +5,8 @@ export interface LatentNeed {
   id: string
   title: string
   tenantCompany?: string
+  /** Nachfrager-Organisation — Empfänger eines Angebots (Demo-Default-Routing: org-mobimo). */
+  tenantOrgId?: string
   assetType: AssetType
   desiredLocation: string
   sizeRange: { min: number; max: number }