fix: parse OpenCode sessions from SQLite storage (opencode.db)

[felipetruman]

Description

Problem

Newer OpenCode versions migrate session storage from the legacy JSON file layout (storage/session/global/*.json + storage/message/ + storage/part/) into a single SQLite database at ~/.local/share/opencode/opencode.db. After that migration the storage/ tree is left nearly empty, so parseOpenCodeSessions silently reports zero OpenCode sessions on any machine running a current OpenCode build.

On my machine this meant 1,143 real OpenCode sessions were invisible to the coach while Claude Code and Codex sessions were picked up fine.

Fix

• parser-opencode.ts: read opencode.db via the node:sqlite builtin (Node >= 22.5). The db stores the same JSON payloads as the legacy files in data columns, minus the id fields, which live in dedicated columns — the reader re-attaches them (message.id/session_id, part.id/message_id/session_id) and surfaces the nested model.modelID as the flat modelID the parser expects. Session rows are plain columns and are mapped to the existing OcSession shape.
• The existing per-session assembly logic is extracted into assembleOpenCodeSession() and shared by both the legacy JSON path and the new SQLite path, so request building, token accounting, and devcontainer detection stay identical.
• node:sqlite is loaded lazily via process.getBuiltinModule and the SQLite source is skipped gracefully when the builtin is unavailable (e.g. older extension hosts). The db is opened read-only and failures fall back to whatever was already parsed, mirroring readJsonSafe's tolerance.
• Legacy JSON sessions win on id collisions, so partially-migrated installs don't double count.
• findOpenCodeDirs now also qualifies an install where only opencode.db exists and the storage/ dir is already gone.

Testing

• New test seeds a real opencode.db (via node:sqlite) with a user → assistant exchange and asserts sessions, requests, token counts, flat model id, and workspace root are parsed; skips when the builtin is unavailable.
• Full suite: 1214 tests pass. tsc --noEmit clean. ESLint: no new errors or warnings in parser-opencode.ts.
• Verified against a real ~750 MB opencode.db: 0 → 1,143 sessions parsed, with Claude Code and Codex counts unchanged.

Related Issues

Fixes #84

Checklist

• npm run check passes (typecheck + lint + spellcheck + knip + tests) — 1214 tests, cspell 0 issues, knip clean, tsc --noEmit clean, ESLint 0 errors
• Changes are covered by tests (new SQLite-layout test seeding a real opencode.db)
• Documentation updated (parser header comment documents both storage layouts)

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[felipetruman]

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