v2.5.8-dev.3

feat(branding): rebrand to Osmium Sound

Replaces all user-visible "HiFi Player" / "HiFi Media Player" strings
with "Osmium Sound" across the app, ISO build, and OTA system.
Internal script names, service names, system paths, and OTA prefixes
are intentionally unchanged to preserve backward compatibility.

Changes:
- Electron app title, productName, setup wizard brand/subtitle
- Android companion app_name
- Plymouth: copies logo.png from repo root instead of generating text
- ISO installer splash and boot menu labels ("Install Osmium Sound")
- GRUB_DISTRIBUTOR set to "Osmium Sound"
- Squeezelite player name: HiFiPlayer → OsmiumSound
- sources_server.py HTML page title
- OS OTA migration 0003: updates squeezelite, GRUB and Plymouth logo
  on existing devices; Plymouth change triggers initramfs regen + reboot

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>