feat: add --review flag with browser-based side-by-side image review

- Launches local HTTP server with dark-themed review UI
- Side-by-side image comparison per duplicate group
- Checkbox selection + delete confirmation
- Shows file size and path per image
- Exact/similar badges per group
- Shutdown endpoint for clean exit
- Magic byte format detection (fixes misnamed screenshots)
- 23 tests passing

Cargo.toml

@@ -8,3 +8,8 @@ image = { version = "0.25", default-features = true, features = ["jpeg", "png",
 sha2 = "0.10"
 walkdir = "2.5"
 anyhow = "1"
+tiny_http = "0.12"
+open = "5"
+base64 = "0.22"
+serde = { version = "1", features = ["derive"] }
+serde_json = "1"