fix: restore sample rate switching and add restart option

[kush2shah]

Builds on top of the v3 log-streaming rework. In testing on macOS 27, v3 detected tracks but never actually switched the device sample rate. This PR fixes that and hardens the process/app lifecycle, and adds a Restart option.

The switching fix (main one)

Music logs the format lines this branch parses — play> cm>> / asbdSampleRate / sdBitDepth — at debug level. log stream withholds debug-level messages unless you explicitly request them, so LogReader was receiving zero entries and nothing ever switched.

Verified directly with the app's exact predicate:

• without --level debug: 0 lines
• with --level debug: full stream, including e.g. ... play> cm>> mediaFormatinfo '<private>' , ... sdFormatID = alac, ... sdBitDepth = 16 bit, asbdSampleRate = 44.1 kHz

After adding the flag, driving track changes shows the pipeline resolving the device format end-to-end (NEAREST FORMAT [...mSampleRate: 44100.0...]).

Other fixes

• Single detection instance. AppDelegate and MenuBarController were each creating their own OutputDevices + MediaRemoteController, so two log readers and two controllers raced to set the device sample rate (and doubled the helper processes). Consolidated to one shared instance owned by AppDelegate.
• Subprocess lifecycle. LogReader now terminates the log stream subprocess on quit/restart (it was previously orphaned), buffers partial pipe reads so a line split across two reads still parses, and respawns the stream if it dies so switching doesn't silently go dead.
• Bounded collection. The per-track format collection no longer grows for the entire lifetime of the app.

New feature

• Restart LosslessSwitcher menu item, alongside Quit. Child processes are torn down in applicationWillTerminate, which both Quit and Restart go through.

Testing

• Builds clean (xcodebuild ... build).
• Launch spawns exactly one log stream subprocess (was two before consolidation).
• Graceful quit leaves no orphaned log stream process.
• Track changes produce detected stats + resolved device format in the app's output.

Note: because these are debug-level logs, this is validated against how Music logs on current macOS; if a future Music build moves the format line to a different category/level the predicate would need revisiting.

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