Add single-instance support and clean up scaffolding files

Ensure only one Vesper instance runs at a time. When a second
instance is launched with a file argument, the file is forwarded
to the existing window. Remove unused template SVGs and test file.

src-tauri/Cargo.lock

@@ -3703,6 +3703,21 @@ dependencies = [
  "zbus",
 ]
 
+[[package]]
+name = "tauri-plugin-single-instance"
+version = "2.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "dc61e4822b8f74d68278e09161d3e3fdd1b14b9eb781e24edccaabf10c420e8c"
+dependencies = [
+ "serde",
+ "serde_json",
+ "tauri",
+ "thiserror 2.0.18",
+ "tracing",
+ "windows-sys 0.60.2",
+ "zbus",
+]
+
 [[package]]
 name = "tauri-runtime"
 version = "2.10.0"
@@ -4281,7 +4296,7 @@ checksum = "0b928f33d975fc6ad9f86c8f283853ad26bdd5b10b7f1542aa2fa15e2289105a"
 
 [[package]]
 name = "vesper"
-version = "0.1.0"
+version = "1.0.1"
 dependencies = [
  "serde",
  "serde_json",
@@ -4290,6 +4305,7 @@ dependencies = [
  "tauri-plugin-dialog",
  "tauri-plugin-fs",
  "tauri-plugin-opener",
+ "tauri-plugin-single-instance",
 ]
 
 [[package]]