README: add basic Mermaid structure map (renders on Gitea home)

README.md

@@ -2,6 +2,32 @@
 
 Find your woof. A return-item tag platform (PetHub/ReturnMe style) — *"Where Woof !"* (a play on *werewolf*). Pre-coded QR/NFC tags on your dog, baggage, skis, etc. A finder scans the tag and sees exactly how to return it — call, text, or leave their number; location is shared with the owner when the finder allows.
 
+## Structure at a glance
+
+```mermaid
+flowchart LR
+  subgraph public["where-woof.com — public (Go + HTMX)"]
+    T[Tag QR/NFC] --> P["GET /t/:code"]
+    P --> S["POST /t/:code/scan"]
+    P --> C[finder contact]
+    O[/order/] --> BUY[Stripe Checkout]
+  end
+  subgraph admin["admin.where-woof.com — Laravel + Filament"]
+    A[Staff manage users/tags/orders/plans]
+    W["POST /webhooks/stripe"] --> D2["orders.status + tag transitions"]
+  end
+  subgraph core["Go frontend .13:3020"]
+    S --> G{"shouldAlert <br/> paid sub · SMS pool · caps"}
+    G -->|pass| SMS["SMSGlobal → owner phone"]
+    G -->|record| DB["Postgres .13:5434"]
+  end
+  BUY --> W
+  A --> DB
+  DB --> D2
+```
+
+*Interactive map:* [maps.lab.audasmedia.com.au/where_woof/docs/](https://maps.lab.audasmedia.com.au/where_woof/docs/diagrams/where-woof-flow.html) · *Source:* `docs/where-woof-flow.mmd`
+
 ## Status
 
 GOAT front-end (Phase 1) built and verified — see `where_woof.md` for the full plan and roadmap.