feat(cache): implement Id3v2Handler for MP3 metadata synthesis

- Implement all 8 FormatHandler trait methods
- Use lofty 0.24 for ID3v2.4 tag creation/parsing
- Map all 36 AudioMeta fields to ID3v2 frames
- Handle ID3v2 header parsing for audio_start
- Detect ID3v1 tags at EOF for audio_end
- Add 13 comprehensive unit tests
- Fix test-utils AudioMeta construction with ..Default::default()
- All tests pass, LSP diagnostics clean

Cargo.lock

@@ -629,6 +629,12 @@ dependencies = [
  "parking_lot_core 0.9.12",
 ]
 
+[[package]]
+name = "data-encoding"
+version = "2.11.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a4ae5f15dda3c708c0ade84bfee31ccab44a3da4f88015ed22f63732abe300c8"
+
 [[package]]
 name = "debugid"
 version = "0.8.0"
@@ -1691,6 +1697,32 @@ dependencies = [
  "scopeguard",
 ]
 
+[[package]]
+name = "lofty"
+version = "0.24.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "dec4feeff6c7d75093278133a06e827d7af6d2bfe20b0f331f9d10338a5ec7ca"
+dependencies = [
+ "byteorder",
+ "data-encoding",
+ "flate2",
+ "lofty_attr",
+ "log",
+ "ogg_pager",
+ "paste",
+]
+
+[[package]]
+name = "lofty_attr"
+version = "0.12.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "458ace39169e4b83c4f77ae3d42d5d1d11c422feef590219a97c973d3b524557"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.117",
+]
+
 [[package]]
 name = "log"
 version = "0.4.29"
@@ -1885,6 +1917,7 @@ version = "0.1.0"
 dependencies = [
  "chrono",
  "image",
+ "lofty",
  "musicfs-cas",
  "musicfs-core",
  "musicfs-metadata",
@@ -2256,6 +2289,15 @@ dependencies = [
  "memchr",
 ]
 
+[[package]]
+name = "ogg_pager"
+version = "0.7.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9d36b1d6964c3ac92b7aea701057e02b6b91143d70d83b20abf75a231a3c0216"
+dependencies = [
+ "byteorder",
+]
+
 [[package]]
 name = "once_cell"
 version = "1.21.4"