Add lightweight dev compose with FakeWallet

Runs just LNbits + Fava — no LND nodes, Bitcoin Core, or Boltz.
For testing extension changes without full regtest overhead.

Usage: docker compose -f docker-compose.dev.yml up -d

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docker-compose.dev.yml

@@ -0,0 +1,38 @@
+# Lightweight LNbits dev environment — FakeWallet, no Lightning nodes
+#
+# Usage:
+#   docker compose -f docker-compose.dev.yml up -d
+#   docker compose -f docker-compose.dev.yml logs -f lnbits
+#   docker compose -f docker-compose.dev.yml down
+#
+# LNbits:  http://localhost:5001
+# Fava:    http://localhost:3333
+
+services:
+  lnbits:
+    hostname: lnbits
+    image: lnbits/lnbits
+    restart: on-failure
+    user: "0:0"
+    environment:
+      LNBITS_PORT: 5001
+      DEBUG: true
+      LNBITS_ADMIN_UI: true
+      LNBITS_BACKEND_WALLET_CLASS: "FakeWallet"
+      LNBITS_DATA_FOLDER: "./data"
+      LNBITS_EXTENSIONS_PATH: "/shared"
+      FAKE_WALLET_SECRET: "devsecret"
+    ports:
+      - 5001:5001
+    volumes:
+      - ./data/lnbits-dev:/app/data
+      - /home/padreug/dev/shared/extensions:/shared/extensions
+
+  fava:
+    hostname: fava
+    build: ./fava
+    restart: on-failure
+    ports:
+      - 3333:5000
+    volumes:
+      - ./data/fava:/bean