chore: move ShareServer development to a standalone repository

Remove the extracted ShareServer prototype and its server-specific documents
from Desktop. Link the shared network architecture to goodbuddy-shareserver,
while retaining Desktop ownership of the cross-product architecture.

Preserve local generated artifacts and ignore the old server build output.
Desktop runtime behavior and released user data are unchanged. Desktop tests,
typecheck, and lint passed; the standalone service was validated separately.

.gitignore

@@ -1,6 +1,8 @@
 node_modules/
 out/
 dist/
+# Local build output left by the extracted ShareServer project.
+shareserver/build-server/
 coverage/
 .vite/
 .runtime-resources/