fix(config): use XDG picture directory as default

Replace hardcoded \"~/Pictures\" with dirs::picture_dir() which resolves
to the actual absolute path (e.g. /home/user/Pictures).

The tilde (~) in paths is not automatically expanded by Rust's PathBuf,
causing path.exists() to return false for \"~/Pictures\".

Using dirs::picture_dir() provides:
- Proper absolute path resolution
- XDG Base Directory compliance
- Fallback to home directory if Pictures doesn't exist

Note: Users with existing config files need to delete
~/.config/cosmic/org.codeberg.wfx.Noctua/v1/default_image_dir
to apply the new default."

Cargo.lock

@@ -1229,7 +1229,7 @@ dependencies = [
  "atomicwrites",
  "cosmic-config-derive",
  "cosmic-settings-daemon",
- "dirs",
+ "dirs 6.0.0",
  "futures-util",
  "iced_futures",
  "known-folders",
@@ -1318,7 +1318,7 @@ dependencies = [
  "almost",
  "cosmic-config",
  "csscolorparser",
- "dirs",
+ "dirs 6.0.0",
  "palette",
  "ron",
  "serde",
@@ -1518,13 +1518,34 @@ dependencies = [
  "crypto-common",
 ]
 
+[[package]]
+name = "dirs"
+version = "5.0.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "44c45a9d03d6676652bcb5e724c7e988de1acad23a711b5217ab9cbecbec2225"
+dependencies = [
+ "dirs-sys 0.4.1",
+]
+
 [[package]]
 name = "dirs"
 version = "6.0.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "c3e8aa94d75141228480295a7d0e7feb620b1a5ad9f12bc40be62411e38cce4e"
 dependencies = [
- "dirs-sys",
+ "dirs-sys 0.5.0",
+]
+
+[[package]]
+name = "dirs-sys"
+version = "0.4.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "520f05a5cbd335fae5a99ff7a6ab8627577660ee5cfd6a94a6a929b52ff0321c"
+dependencies = [
+ "libc",
+ "option-ext",
+ "redox_users 0.4.6",
+ "windows-sys 0.48.0",
 ]
 
 [[package]]
@@ -1535,7 +1556,7 @@ checksum = "e01a3366d27ee9890022452ee61b2b63a67e6f13f58900b651ff5665f0bb1fab"
 dependencies = [
  "libc",
  "option-ext",
- "redox_users",
+ "redox_users 0.5.2",
  "windows-sys 0.61.2",
 ]
 
@@ -3610,6 +3631,7 @@ version = "0.1.0"
 dependencies = [
  "anyhow",
  "clap",
+ "dirs 5.0.1",
  "env_logger",
  "futures-util",
  "i18n-embed",
@@ -4793,6 +4815,17 @@ dependencies = [
  "bitflags 2.10.0",
 ]
 
+[[package]]
+name = "redox_users"
+version = "0.4.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ba009ff324d1fc1b900bd1fdb31564febe58a8ccc8a6fdbb93b543d33b13ca43"
+dependencies = [
+ "getrandom 0.2.16",
+ "libredox",
+ "thiserror 1.0.69",
+]
+
 [[package]]
 name = "redox_users"
 version = "0.5.2"