feat: add startup diagnostics for environment issues

- Log HOME, PATH, XDG_DATA_HOME at startup
- Warn when critical env vars are missing
- Log item count per provider after refresh

This helps diagnose why items may not load when launched
from window manager keybinds vs terminal.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "owlry"
-version = "0.1.2"
+version = "0.1.3"
 edition = "2024"
 rust-version = "1.90"
 description = "A lightweight, owl-themed application launcher for Wayland"