release: rebuild .deb with cross-distro pkexec dependency

On Debian 13 (trixie), policykit-1 was retired and pkexec moved
into a standalone package. The previous Depends: policykit-1
made `apt install` fail with \"none of the choices are installable\"
on a fresh trixie VM.

Switch to Depends: pkexec | policykit-1 so apt can satisfy the
constraint on both:
  - bookworm: policykit-1 (which provides /usr/bin/pkexec)
  - trixie:   pkexec (standalone)

Also updates SHA256SUMS and the install README accordingly.

release/README.md

@@ -8,7 +8,9 @@ Pre-built `.deb` of the mycellium-ui desktop client. Tested on Debian 12 (bookwo
 sudo apt install ./mycellium-ui_0.1.0_amd64.deb
 ```
 
-`apt install` with a local path resolves runtime deps (`policykit-1`, `libwebkit2gtk-4.1-0`, `libgtk-3-0`) automatically. Plain `dpkg -i` will fail if any of those are missing.
+`apt install` with a local path resolves runtime deps (`pkexec` or `policykit-1` depending on the distro, `libwebkit2gtk-4.1-0`, `libgtk-3-0`) automatically. Plain `dpkg -i` will fail if any of those are missing.
+
+The `pkexec | policykit-1` alternative covers both Debian 12 (where `pkexec` ships inside `policykit-1`) and Debian 13 (where `pkexec` is a standalone package).
 
 ## Verify
 

release/SHA256SUMS

@@ -1 +1 @@
-c85a2f6584949bd04a2a56b7fc3a5f7ed6e99c3291dec6c7eef99e8b28a0b2be  release/mycellium-ui_0.1.0_amd64.deb
+a5df5c25c2fb13ff7d3486c6214371dac540ccaa70094e02e458bfd0b5e6b367  release/mycellium-ui_0.1.0_amd64.deb

src-tauri/tauri.conf.json

@@ -40,7 +40,7 @@
     "externalBin": ["binaries/mycelium"],
     "linux": {
       "deb": {
-        "depends": ["policykit-1"],
+        "depends": ["pkexec | policykit-1"],
         "files": {
           "/usr/share/polkit-1/actions/tech.threefold.mycellium-ui.policy": "packaging/polkit/tech.threefold.mycellium-ui.policy"
         }