feat: support Quectel USB identity and multiple DJI modules

[vvusu]

Summary

• support both the original DJI 2ca3:4006 identity and the Quectel-compatible 2c7c:0125 identity
• enumerate identical modules by macOS USB locationID and open the selected physical device through libusb
• add a compact responsive module selector to the web UI
• isolate per-device SMS caches and rebuild eSIM sessions when switching modules
• document multi-module usage and add USB identity/location grouping tests

Hardware verification

• detected two connected 2c7c:0125 modules at distinct USB locations
• opened the AT bulk interface independently on both modules
• verified AT returns OK after A -> B -> A switching
• verified both SIMs are inserted and registered on LTE
• verified eSIM inventories remain distinct between modules

Test plan

• go test ./...
• go vet ./...
• go test -race ./cmd/djonehub-macos
• node --check cmd/djonehub-macos/web/app.js
• git diff --check origin/main...HEAD

Closes #5