ci(release): re-sign updater tarball after tauri-action's repack

tauri-action always re-packs Psysonic.app into .app.tar.gz after tauri
CLI finishes (regardless of includeUpdaterJson), so the .sig that tauri
CLI produces never matches the final tarball — and the sig tauri-action
was supposed to produce silently goes missing ("Signature not found for
the updater JSON. Skipping upload...").

Rather than fight the repack, sign the repacked tarball ourselves in a
follow-up step using `tauri signer sign` against the same private key
(from TAURI_SIGNING_PRIVATE_KEY), then upload the fresh .sig. tauri-
action still handles the DMG + .app.tar.gz upload; we only add the .sig.

Also removes an unused `std::rc::Rc` import in the vendored cpal patch.

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

src-tauri/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "psysonic"
-version = "1.34.18"
+version = "1.34.19"
 description = "Psysonic Desktop Music Player"
 authors = []
 license = ""