docs(core): update paths.ts top-comment for XDG resolution (T303)

T303 — Wave 1 of T299 v2026.4.11 epic.

Stale top-of-file comment said "default: ~/.cleo" but the code resolves
via env-paths XDG. Comment now lists per-OS examples (Linux/macOS/Windows).

Also deletes the 0-byte stray .cleo/cleo.db (untracked, unreferenced).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: kryptobaseddev

packages/core/src/paths.ts

@@ -1,8 +1,14 @@
 /**
  * XDG-compliant path resolution for CLEO V2.
  *
+ * Global data directory is resolved via env-paths (XDG on Linux, platform
+ * conventions on macOS and Windows):
+ *   Linux:   ~/.local/share/cleo
+ *   macOS:   ~/Library/Application Support/cleo
+ *   Windows: %LOCALAPPDATA%\cleo
+ *
  * Environment variables:
- *   CLEO_HOME   - Global installation directory (default: ~/.cleo)
+ *   CLEO_HOME   - Override global installation directory
  *   CLEO_DIR    - Project data directory (default: .cleo)
  *
  * @epic T4454