fix(scan): quiet startup scans & thumbnail RAW/HEIC

Three recurring issues on every full scan:

1. Video playlist scans re-enqueued every file only to reject it as
   AlreadyExists. Pre-filter in ScanDirectoryMessage and QueueVideosMessage
   so we skip videos whose .m3u8 already exists, and demote the leaked
   AlreadyExists log to debug.

2. image crate was built with only jpeg/png features, so webp/tiff/avif
   files logged "format not supported" every scan. Enable those features.

3. RAW (ARW/NEF/CR2/...) and HEIC thumbnails weren't generated, so the
   scan kept retrying them. Try the file's embedded JPEG preview via
   kamadak-exif first (fast, pure-Rust, works on Sony ARW where ffmpeg's
   TIFF decoder fails). Fall back to ffmpeg for HEIC/HEIF and RAWs with
   no preview. Anything still undecodable gets a <thumb>.unsupported
   sentinel so future scans skip it.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Cargo.lock

@@ -908,6 +908,12 @@ version = "0.8.21"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "d0a5c400df2834b80a4c3327b3aad3a4c4cd4de0629063962b03235697506a28"
 
+[[package]]
+name = "crunchy"
+version = "0.2.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "460fbee9c2c2f33933d720630a6a0bac33ba7053db5344fac858d4b8952d77d5"
+
 [[package]]
 name = "crypto-common"
 version = "0.1.6"
@@ -1218,6 +1224,26 @@ version = "2.3.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "37909eebbb50d72f9059c3b6d82c0463f2ff062c9e95845c43a6c9c0355411be"
 
+[[package]]
+name = "fax"
+version = "0.2.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f05de7d48f37cd6730705cbca900770cab77a89f413d23e100ad7fad7795a0ab"
+dependencies = [
+ "fax_derive",
+]
+
+[[package]]
+name = "fax_derive"
+version = "0.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a0aca10fb742cb43f9e7bb8467c91aa9bcb8e3ffbc6a6f7389bb93ffc920577d"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
 [[package]]
 name = "fdeflate"
 version = "0.3.7"
@@ -1501,6 +1527,17 @@ dependencies = [
  "tracing",
 ]
 
+[[package]]
+name = "half"
+version = "2.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6ea2d84b969582b4b1864a92dc5d27cd2b77b622a8d79306834f1be5ba20d84b"
+dependencies = [
+ "cfg-if",
+ "crunchy",
+ "zerocopy",
+]
+
 [[package]]
 name = "hashbrown"
 version = "0.14.5"
@@ -1843,11 +1880,14 @@ checksum = "1c6a3ce16143778e24df6f95365f12ed105425b22abefd289dd88a64bab59605"
 dependencies = [
  "bytemuck",
  "byteorder-lite",
+ "image-webp",
  "moxcms",
  "num-traits",
  "png",
  "ravif",
  "rayon",
+ "rgb",
+ "tiff",
  "zune-core",
  "zune-jpeg",
 ]
@@ -1908,6 +1948,16 @@ dependencies = [
  "zerocopy",
 ]
 
+[[package]]
+name = "image-webp"
+version = "0.2.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "525e9ff3e1a4be2fbea1fdf0e98686a6d98b4d8f937e1bf7402245af1909e8c3"
+dependencies = [
+ "byteorder-lite",
+ "quick-error",
+]
+
 [[package]]
 name = "imgref"
 version = "1.11.0"
@@ -3712,6 +3762,20 @@ dependencies = [
  "syn",
 ]
 
+[[package]]
+name = "tiff"
+version = "0.10.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "af9605de7fee8d9551863fd692cce7637f548dbd9db9180fcc07ccc6d26c336f"
+dependencies = [
+ "fax",
+ "flate2",
+ "half",
+ "quick-error",
+ "weezl",
+ "zune-jpeg",
+]
+
 [[package]]
 name = "time"
 version = "0.3.42"
@@ -4269,6 +4333,12 @@ dependencies = [
  "wasm-bindgen",
 ]
 
+[[package]]
+name = "weezl"
+version = "0.1.12"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a28ac98ddc8b9274cb41bb4d9d4d5c425b6020c50c46f25559911905610b4a88"
+
 [[package]]
 name = "winapi"
 version = "0.3.9"