OpenCode sessions are not loaded from SQLite storage

[aymenfurter]

Description

Current OpenCode versions store session data in ~/.local/share/opencode/opencode.db. AI Engineering Coach searches the legacy JSON storage directories. As a result, it can report zero OpenCode sessions without an error.

Reported in PR #170. Related to #84.

Steps to Reproduce

1. Use an OpenCode version that stores sessions in opencode.db.
2. Create one or more OpenCode sessions.
3. Open AI Engineering Coach.
4. Load the session data.
5. Observe that no OpenCode sessions appear.

Expected Behavior

The extension reads opencode.db in read-only mode and shows the OpenCode sessions, requests, token counts, and model information.

Legacy JSON storage must continue to work.

Extension Version

Not provided in PR #170.

VS Code Version

Not provided in PR #170.

Operating System

Not provided in PR #170.