Simplify desktop release pipeline: single build, no process smoke test

Replace the 855-line managed-daemon-smoke.mjs (which spawned relay
servers, daemons, and tested E2E connectivity in CI) with a fast
validate-managed-runtime.mjs that checks the bundle is correctly
assembled without launching any processes.

Structural changes:
- Eliminate double-build: removed the pre-build step that compiled the
  Tauri app just for smoke testing before tauri-action rebuilt it
- Move version-setting before the build so there's no version confusion
- Sign managed runtime before tauri-action build (macOS)
- Smoke tags now do a real tauri build instead of --no-bundle, giving
  actual signal about whether the release would succeed
- Reduce each platform job from ~15 steps to ~12

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

packages/desktop/package.json

@@ -8,6 +8,7 @@
     "prepare:managed-runtime": "npm --prefix ../.. run build:daemon && npm run build:managed-runtime",
     "dev": "npm run prepare:managed-runtime && tauri dev",
     "build": "npm --prefix ../.. run build:web --workspace=@getpaseo/app && npm run prepare:managed-runtime && tauri build",
+    "validate:managed-runtime": "node ./scripts/validate-managed-runtime.mjs",
     "smoke:managed-daemon": "node ./scripts/managed-daemon-smoke.mjs",
     "tauri": "tauri"
   },