DSH Desktop v0.1.0

Correct the signing-secret instructions that broke the first release

README told you to set TAURI_SIGNING_PRIVATE_KEY_PASSWORD to "an empty string".
GitHub does not accept an empty secret value, so following that instruction means
putting *something* in the field -- a space, in this case. Tauri treats any
non-empty value as a real password and tries to decrypt a key that has none:

    failed to decode secret key: incorrect updater private key password:
    Wrong password for that key

That is what failed the v0.1.0 release run. Reproduced locally with a single space
to confirm, rather than inferring it from the step list: the run's logs need auth
to download, so the only evidence from CI was "tauri-action failed after npm ci
succeeded".

The failure is easy to misread, which is worth writing down: the installer builds
fine and is reported as built, then signing errors afterwards. So "the bundle
succeeded" says nothing about whether the release will work.

Correct instruction is to create only TAURI_SIGNING_PRIVATE_KEY. The workflow keeps
referencing the password variable; with no such secret it resolves to an empty
string, which is the state a passwordless key needs -- and the state my local
builds were always in, which is why this never showed up until CI ran it.

Also documented in the English README, since anyone forking this hits it too.

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