Add Nav map camera stream entity (v2)

[MTrab]

Description

• Add a second camera entity (nav_map) that streams rendered NavMap PNG frames
• Keep existing vision camera intact
• Add coordinator nav-map stream loop with reconnect/auth handling similar to existing camera flow
• Track latest robot state to pass pose overlay provider into navmap frame rendering
• Update user-facing camera translations (Nav map) and README feature text
• Point integration dependency to pyddlvector branch feat/navmap-frame-feed for this test cycle

Test strategy

• ruff check custom_components/vector/coordinator.py custom_components/vector/camera.py tests/test_camera.py custom_components/vector/strings.json custom_components/vector/translations/en.json
• pytest -q tests/test_camera.py tests/test_coordinator.py tests/test_init.py

Known limitations

• Nav-map frames depend on robot/firmware providing NavMapFeed; if not available, camera falls back to unknown image

Required configuration changes

• None