feat(watcher): adaptive filesystem watchdog with zero CPU when idle

Monitors all registered folders using OS-native events (ReadDirectoryChangesW
on Windows) so new, modified, and deleted files are reflected in the gallery
automatically without manual reindexing.

Key design points:
- Adaptive blocking: recv() when no events pending (zero CPU), switches to
  recv_timeout(earliest_deadline) only when debounce timers are running — wakes
  exactly when the soonest event is ready, no busy-polling
- 500 ms per-path debounce coalesces rapid OS event bursts into one action
- Change detection preserved: build_record skips upsert if file_size + mtime
  unchanged, preventing spurious thumbnail/embedding re-queues and avoiding
  clobbering of existing metadata like thumbnail_path
- Access events (reads) filtered out; only Create/Modify/Remove trigger work
- Deletion path: emits watcher-deleted event with image IDs; frontend removes
  those images from state and clears selectedImage if it was deleted

WatcherHandle stored in app state; add_folder / remove_folder / update_folder_path
commands keep the watched path set in sync with the DB.

src-tauri/Cargo.lock

@@ -1750,6 +1750,15 @@ dependencies = [
  "winapi",
 ]
 
+[[package]]
+name = "fsevent-sys"
+version = "4.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "76ee7a02da4d231650c7cea31349b889be2f45ddb3ef3032d2ec8185f6313fd2"
+dependencies = [
+ "libc",
+]
+
 [[package]]
 name = "futf"
 version = "0.1.5"
@@ -2932,6 +2941,26 @@ dependencies = [
  "cfb",
 ]
 
+[[package]]
+name = "inotify"
+version = "0.9.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f8069d3ec154eb856955c1c0fbffefbf5f3c40a104ec912d4797314c1801abff"
+dependencies = [
+ "bitflags 1.3.2",
+ "inotify-sys",
+ "libc",
+]
+
+[[package]]
+name = "inotify-sys"
+version = "0.1.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e05c02b5e89bff3b946cedeca278abc628fe811e604f027c45a8aa3cf793d0eb"
+dependencies = [
+ "libc",
+]
+
 [[package]]
 name = "ipnet"
 version = "2.12.0"
@@ -3133,6 +3162,26 @@ dependencies = [
  "unicode-segmentation",
 ]
 
+[[package]]
+name = "kqueue"
+version = "1.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "273c0752728918e0ac4976f2b275b6fefb9ecd400585dec929419f3844cd87b5"
+dependencies = [
+ "kqueue-sys",
+ "libc",
+]
+
+[[package]]
+name = "kqueue-sys"
+version = "1.1.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "07293a4e297ac234359b510362495713f75ea345d5307140414f20c69ffeb087"
+dependencies = [
+ "bitflags 2.11.0",
+ "libc",
+]
+
 [[package]]
 name = "kuchikiki"
 version = "0.8.8-speedreader"
@@ -3438,6 +3487,18 @@ dependencies = [
  "simd-adler32",
 ]
 
+[[package]]
+name = "mio"
+version = "0.8.11"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a4a650543ca06a924e8b371db273b2756685faae30f8487da1b56505a8f78b0c"
+dependencies = [
+ "libc",
+ "log",
+ "wasi 0.11.1+wasi-snapshot-preview1",
+ "windows-sys 0.48.0",
+]
+
 [[package]]
 name = "mio"
 version = "1.2.0"
@@ -3621,6 +3682,25 @@ dependencies = [
  "minimal-lexical",
 ]
 
+[[package]]
+name = "notify"
+version = "6.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6205bd8bb1e454ad2e27422015fb5e4f2bcc7e08fa8f27058670d208324a4d2d"
+dependencies = [
+ "bitflags 2.11.0",
+ "crossbeam-channel",
+ "filetime",
+ "fsevent-sys",
+ "inotify",
+ "kqueue",
+ "libc",
+ "log",
+ "mio 0.8.11",
+ "walkdir",
+ "windows-sys 0.48.0",
+]
+
 [[package]]
 name = "notify-rust"
 version = "4.17.0"
@@ -4308,6 +4388,7 @@ dependencies = [
  "kamadak-exif",
  "log",
  "memmap2",
+ "notify",
  "ort",
  "r2d2",
  "r2d2_sqlite",
@@ -6392,7 +6473,7 @@ checksum = "2bd1c4c0fc4a7ab90fc15ef6daaa3ec3b893f004f915f2392557ed23237820cd"
 dependencies = [
  "bytes",
  "libc",
- "mio",
+ "mio 1.2.0",
  "parking_lot",
  "pin-project-lite",
  "signal-hook-registry",
@@ -7519,6 +7600,15 @@ dependencies = [
  "windows-targets 0.42.2",
 ]
 
+[[package]]
+name = "windows-sys"
+version = "0.48.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "677d2418bec65e3338edb076e806bc1ec15693c5d0104683f2efe857f61056a9"
+dependencies = [
+ "windows-targets 0.48.5",
+]
+
 [[package]]
 name = "windows-sys"
 version = "0.52.0"