fix(updater): per-user NSIS Windows updates + skip auto-update in dev

[its-mash]

What

Fixes the Windows auto-updater so it no longer requires admin and no longer "crashes" (the app exiting to apply an update it can't apply), and stops dev builds from auto-updating over your local changes.

Root cause

The updater shipped a per-machine MSI installed in quiet mode. Per-machine MSI upgrades need elevation; quiet suppresses the UAC prompt; apps run non-elevated by default — so the silent install failed (1603 / "must be Administrator", 1730). Because downloadAndInstall() quits the app to apply the update, it looked like a crash/loop. This hit any non-elevated user on auto-update (auto-install defaults to on), not just pnpm dev.

Changes (apps/desktop/src-tauri/tauri.conf.json, apps/desktop/src/App.tsx)

• Drop msi from bundle.targets (was "all" → explicit list). Windows now ships NSIS only, already configured per-user (nsis.installMode: "currentUser"), so updates install without elevation.
• installMode: "quiet" → "passive" — shows a small progress UI and surfaces a UAC prompt if elevation is ever needed, instead of failing invisibly. With per-user NSIS the normal path still needs no elevation.
• Skip the startup auto-update under pnpm dev (if (import.meta.env.DEV) return;) — a dev build would otherwise detect a newer published release, install it over the dev build, and relaunch, so local changes never appear. Production unaffected.

No worker change needed

The api.mcpmux.com resolver (pinManifestUrls) rewrites manifest URLs filename-agnostically (path prefix only), so once releases build NSIS-only, latest.json will reference the -setup.exe and the resolver passes it straight through. Verified the prerelease channel resolves correctly (0.4.0-191) — an earlier "wrong version" observation was a bad manual test (header value pre instead of prerelease), not a resolver bug.

Tests

App update-banner suite stubs import.meta.env.DEV=false to keep exercising the production flow — all 12 pass. tsc --noEmit clean; ESLint clean (only pre-existing warnings); clippy/fmt clean via pre-commit.

Takes effect

On the next release build (the artifact type is decided at build time). Existing per-machine MSI installs will likely need one manual reinstall via the NSIS -setup.exe to fully migrate off the per-machine install.

Follow-up (not in this PR)

• Verify the discover.ui download page doesn't hardcode a .msi asset URL (would 404 once MSI is no longer built).

[its-mash]

Consolidated into #171 per request (single branch, trimmed descriptions).