ci(release): upload updater .sig as release asset

tauri-action on macOS cross-target builds produces the .app.tar.gz.sig
locally but silently skips its upload ("Signature not found for the
updater JSON. Skipping upload..."), which caused generate-manifest to
abort on v1.34.15 because the .sig asset was absent.

New step after tauri-action locates the .sig under src-tauri/target/*/
release/bundle/macos/ and uploads it as Psysonic_aarch64.app.tar.gz.sig
or Psysonic_x64.app.tar.gz.sig — the exact filenames generate-update-
manifest.js expects.

Also bumps version to 1.34.16.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src-tauri/Cargo.lock

@@ -3653,7 +3653,7 @@ dependencies = [
 
 [[package]]
 name = "psysonic"
-version = "1.34.15"
+version = "1.34.16"
 dependencies = [
  "biquad",
  "discord-rich-presence",

src-tauri/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "psysonic"
-version = "1.34.15"
+version = "1.34.16"
 description = "Psysonic Desktop Music Player"
 authors = []
 license = ""

src-tauri/tauri.conf.json

@@ -1,7 +1,7 @@
 {
   "$schema": "https://schema.tauri.app/config/2",
   "productName": "Psysonic",
-  "version": "1.34.15",
+  "version": "1.34.16",
   "identifier": "dev.psysonic.player",
   "build": {
     "beforeDevCommand": "npm run dev",