Add folder scan with format selection; validate A3 on a real library

Library setup as the user described it: pick a folder, choose which RAW
types to look for, scan recursively.

  dr-types::FormatFilter  the tick-box selection, seeing through VFS
                          placeholder suffixes so a dehydrated CR2 still
                          matches as a CR2
  dr-sync::scan           recursive walk, Depth:1 per directory, pruning
                          unchanged subtrees where the backend propagates
                          directory ETags

Verified against nextcloud.tourolle.paris (34.0.2) on a real library:

  browse root      32 entries, 98ms
  scan PhotosRaw   17,185 RAW files in 334 directories, 34.1s
                   (7,836 CR2 + 9,349 DNG)
  range read       262KB of a 21.5MB DNG in 119ms — 1.22% of the file,
                   and enough to read "Canon EOS 6D | ISO 100"

That last line is assumption A3 validated on real data. Cataloguing this
library by whole-file fetch would move roughly 370GB; the range path
moves a few MB.

Pruning is capability-gated rather than assumed: with per-entry ETags a
probe costs a request and proves nothing about children, so it is skipped
entirely. A test asserts zero probes in that case.

Still unresolved: /core/preview returns 400 for every parameter
combination tried, including on a JPEG the server reports as having a
preview. Not a request-shape bug — it fails identically bare. Recorded
rather than worked around; ARCH §6.7 already treats server previews as
opportunistic, so nothing depends on it.

Cargo.lock

@@ -1166,6 +1166,16 @@ version = "0.1.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "d8b14ccef22fc6f5a8f4d7d768562a182c04ce9a3b3157b91390b52ddfdf1a76"
 
+[[package]]
+name = "dr-catalog"
+version = "0.1.0"
+dependencies = [
+ "dr-types",
+ "log",
+ "rusqlite",
+ "thiserror 2.0.20",
+]
+
 [[package]]
 name = "dr-decode"
 version = "0.1.0"
@@ -1209,6 +1219,7 @@ dependencies = [
  "dr-types",
  "log",
  "thiserror 2.0.20",
+ "tokio",
 ]
 
 [[package]]
@@ -1455,6 +1466,18 @@ dependencies = [
  "zune-inflate",
 ]
 
+[[package]]
+name = "fallible-iterator"
+version = "0.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2acce4a10f12dc2fb14a218589d4f1f62ef011b2d0cc4b3cb1bba8e94da14649"
+
+[[package]]
+name = "fallible-streaming-iterator"
+version = "0.1.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7360491ce676a36bf9bb3c56c1aa791658183a54d2744120f27285738d90465a"
+
 [[package]]
 name = "fastrand"
 version = "2.5.0"
@@ -2069,6 +2092,15 @@ dependencies = [
  "foldhash 0.2.0",
 ]
 
+[[package]]
+name = "hashlink"
+version = "0.12.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "32069d97bb81e38fa67eab65e3393bf804bb85969f2bc06bf13f64aef5aba248"
+dependencies = [
+ "hashbrown 0.17.1",
+]
+
 [[package]]
 name = "heck"
 version = "0.5.0"
@@ -3239,6 +3271,17 @@ dependencies = [
  "redox_syscall 0.9.1",
 ]
 
+[[package]]
+name = "libsqlite3-sys"
+version = "0.38.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f1d20bef17f513b9b3004532233187769cd072d790971f4e4da0e346eb6401e8"
+dependencies = [
+ "cc",
+ "pkg-config",
+ "vcpkg",
+]
+
 [[package]]
 name = "libudev-sys"
 version = "0.1.4"
@@ -4923,6 +4966,31 @@ dependencies = [
  "unicode-width 0.2.2",
 ]
 
+[[package]]
+name = "rsqlite-vfs"
+version = "0.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c51c9ae4df8a7fba42103df5c621fa3c37eccf3a3c650879e90fc48b11cc192c"
+dependencies = [
+ "hashbrown 0.16.1",
+ "thiserror 2.0.20",
+]
+
+[[package]]
+name = "rusqlite"
+version = "0.40.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "23f2a97da3e3873c73cb2a2e71b35c40ff95e0b1eefa8d72d8499a6928c3b5b3"
+dependencies = [
+ "bitflags 2.13.1",
+ "fallible-iterator",
+ "fallible-streaming-iterator",
+ "hashlink",
+ "libsqlite3-sys",
+ "smallvec",
+ "sqlite-wasm-rs",
+]
+
 [[package]]
 name = "rustc-demangle"
 version = "0.1.28"
@@ -5568,6 +5636,18 @@ dependencies = [
  "bitflags 2.13.1",
 ]
 
+[[package]]
+name = "sqlite-wasm-rs"
+version = "0.5.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "dc3efc0da82635d7e1ced0053bbbfa8c7ab9645d0bf36ceb4f7127bb85315d75"
+dependencies = [
+ "cc",
+ "js-sys",
+ "rsqlite-vfs",
+ "wasm-bindgen",
+]
+
 [[package]]
 name = "stable_deref_trait"
 version = "1.2.1"
@@ -6333,6 +6413,12 @@ dependencies = [
  "wasm-bindgen",
 ]
 
+[[package]]
+name = "vcpkg"
+version = "0.2.15"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "accd4ea62f7bb7a82fe23066fb0957d48ef677f6eeb8215f372f52e48bb32426"
+
 [[package]]
 name = "version_check"
 version = "0.9.5"