feat(api): add mobile device categories

[Seungpyo1007]

Summary

• add shared tablet, watch, and PDA models plus list/detail routers
• seed and dump the new mobile-device collections from TechAPI data
• keep smartphone variant metadata fields available for future grouped records
• add integration coverage for new endpoints and compact dump generation

Verification

• python -m app.validate
• python -m pytest tests\integration\test_mobile_devices.py tests\integration\test_dump.py tests\integration\test_smartphones.py --basetemp ...tmp\pytest-api-rebase
• git diff --check

Closes #1