feat: omnibox live server search + cross-platform build fix

[ehorizon7]

Changes

Omnibox: live server search

The omnibox previously only searched a local cache, which is empty on fresh installs
and only grows as links are saved through the extension. This meant new users got no
suggestions until they'd built up a cache.

This adds a live call to /api/v1/search on each omnibox input (2+ characters),
merging server results with cached results (deduped by URL). If the server is
unreachable it silently falls back to the local cache, preserving existing behavior.

Cross-platform build script

Replaced the Unix-only cp command in the build script with a Node.js
fs.copyFileSync call so npm run build works correctly on Windows without
a manual copy step.