fix: replace worker pool with semaphore to prevent deadlock in recurs…

[jbuhagiar88]

…ive dir scan

The previous fixed-size worker pool pattern caused deadlocks when recursive directory scanning submitted tasks faster than workers could consume them. The pool's task channel would block, causing all goroutines to stall.

Changes:

• worker.go: Replace Pool (fixed goroutines + task channel) with Semaphore (unlimited goroutines, N concurrent). Semaphore allows each submitted task to spawn its own goroutine immediately, avoiding channel backpressure. Pool type retained for backward compatibility; Stop() is now a no-op.
• run.go: Buffer the gOut channel (10000) so folder scanning goroutines don't block waiting for the upload consumer. Removes go wrapper around pool.Submit() since Submit() now spawns its own goroutine internally.

Tested against large library (100k+ files) — no deadlock observed.