chore: dev environment — signet testnet stack, mock LND RPCs, faucet button

Switch docker-compose from regtest to signet, add standalone testnet stack
(docker-compose.testnet.yml) with Bitcoin+LND+ThunderHub+Fedimint. Mock
backend now auto-detects Podman/Docker sockets and includes full LND/Lightning
RPC mocks. Dev scripts refactored with boot mode, testnet option, and macOS
EAGAIN fix for port cleanup. Added dev faucet button to Home.vue.

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

testnet/thunderhub-config.yaml

@@ -0,0 +1,8 @@
+# ThunderHub account config — connects to LND signet node
+# The LND data volume is mounted read-only at /lnd-data
+masterPassword: "thunderhub"
+accounts:
+  - name: "Archy Signet"
+    serverUrl: "lnd-signet:10009"
+    macaroonPath: "/lnd-data/data/chain/bitcoin/signet/admin.macaroon"
+    certificatePath: "/lnd-data/tls.cert"