feat: add stable camera UUIDs

[matteius]

Summary

• add an immutable, database-generated UUID to every configured camera
• backfill existing stream rows with distinct UUIDv4 identities
• expose camera_uuid in list, detail, full-detail, creation, and configuration-backup responses
• add lookup by UUID while retaining all name-based APIs
• hydrate runtime/config/ONVIF-created streams from the database-owned identity

Stack

Stacked on #496. This is Fleet 01 P0, slice 1; locations, normalized tags, and selectors will follow in separate PRs. Migration 0048 avoids the 0047 number already in active recording-history optimization work.

Validation

• test_config
• test_db_streams
• test_api_handlers_system
• legacy-row migration smoke test: two rows backfilled to two distinct 36-character UUIDv4 values
• git diff --check