feat: add local and room volume modes

[chinmaykrishnroy]

Summary

• adds a Local / Room volume toggle
• defaults clients to Room volume so synced room volume remains visible by default
• lets users switch to Local volume for per-device loudness control
• allows admins to change Room volume while non-admins can view it
• prevents Room volume from capping Local volume after switching modes
• keeps the Room slider synced when admins update room volume

Fixes #99

Testing

• ran bun run build --filter=client
• manually tested Local vs Room volume behavior

Preview

Optional self-hosted preview: https://beatsync.prefect-sys.online/

Note: this preview is my self-hosted deployment and may include local deployment-specific configuration, but the PR itself only changes the Local / Room volume behavior.

[vercel]

@chinmaykrishnroy is attempting to deploy a commit to the freemanjiang's projects Team on Vercel.

A member of the Team first needs to authorize it.

[chinmaykrishnroy]

The Vercel checks appear to need maintainer authorization because this PR comes from my fork.

For verification, I ran bun run build --filter=client locally and manually tested the Local / Room volume behavior. I also included an optional self-hosted preview link in the PR description.