fix: replace notify-debouncer-full/mini with raw notify + custom debounce

notify-debouncer-full cancelled FSEvents Create+Remove pairs (breaking
macOS file deletion detection). notify-debouncer-mini lacked event kind
information (breaking Windows rename detection).

Use raw notify::RecommendedWatcher with a simple 50ms debounce thread
that preserves full event kinds (Create/Write/Remove/Rename). This
matches upstream Rojo's approach (notify v4 built-in debouncer) while
staying on notify v8.

All 489 tests passing on macOS. No debouncer dependencies needed.

Cargo.lock

@@ -1911,7 +1911,6 @@ dependencies = [
  "fs-err",
  "log",
  "notify",
- "notify-debouncer-mini",
  "serde",
  "tempfile",
 ]
@@ -1981,18 +1980,6 @@ dependencies = [
  "windows-sys 0.60.2",
 ]
 
-[[package]]
-name = "notify-debouncer-mini"
-version = "0.7.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "17849edfaabd9a5fef1c606d99cfc615a8e99f7ac4366406d86c7942a3184cf2"
-dependencies = [
- "log",
- "notify",
- "notify-types",
- "tempfile",
-]
-
 [[package]]
 name = "notify-types"
 version = "2.1.0"