fix: avoid hardcoded local service URLs across renderer and libraries

[ubugeeei]

Finding

Backend and renderer URLs are hardcoded in several places, making port collisions and test environments fragile.

Evidence

• electron/main.ts waits on http://127.0.0.1:3000/healthz.
• src/lib/sound/sound.tsx uses http://localhost:3000/audio/meta.
• render/src/main.rs defaults to http://127.0.0.1:3000 endpoints and http://localhost:5174/render.

Acceptance criteria

• Centralize service URL configuration.
• Support environment override in dev and packaged modes.
• Keep existing defaults for backward compatibility.

[ubugeeei]

対応済みです。修正は PR #1 / commit 9cf4498 に反映済みです。