fix: desktop app binary missing from CI release; add prebuilt binary docs

wails build -o with a relative path doesn't resolve against the shell's
CWD — Wails joins it onto its own build/bin/ output dir, so the binary
landed in cmd/app/dist/ instead of the top-level dist/ the release step
globs. Build with the default name and cp it into dist/ explicitly.

Also document how to download and run the prebuilt daemon/anchor
release binaries on Linux, macOS, and Windows.

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

.gitea/workflows/build.yml

@@ -68,7 +68,8 @@ jobs:
       - name: Build desktop app
         run: |
           cd cmd/app
-          wails build -trimpath -ldflags="-s -w" -tags webkit2_41 -o ../../dist/waste-linux-amd64
+          wails build -trimpath -ldflags="-s -w" -tags webkit2_41
+          cp build/bin/waste ../../dist/waste-linux-amd64
 
       # ── Publish release (tags only) ─────────────────────────────────────────